Serotonin

It is also known as 5-Hydroxy Tryptamine. It is an indole-ethylamine.
Synthesis:

Mechanism of action:
Seven families of 5-HT receptor sub-types (subscripts 1-7) are there. They act through a variety of cell membrane receptors that include:
1. Six involved G-protein coupled receptors.
2. One uses ligand gated ion channels.

Action:
It acts as a neurotransmitter causing strong inhibitory effect. It acts on chemosensitive endings causing bradycardia and hypotension. It can cause aggregation of platelets. It may cause hyperventilation due to chemoreceptor reflex.

Clinical uses of serotonin analogues:
1. Buspirone (a 5-HT1A agonist) is used as non-benzodiazepine anxiolytic.
2. Sumatriptan can be used in acute migraine and cluster headache.
3. Appetite suppression appears to be caused by the agonist action at 5-HT2C receptors in the central nervous system.
4. Cisapride (a 5-HT4 agonist) was used for gastroesophageal reflux disease and motility disorders.

Headache

Headache is of three types:

1. Cluster Headache
2. Tension type headache
3. Migraine headache

Characteristics of Cluster Headache:
1. Males are more often attacked by this than females.
2. It usually occurs during sleep.
3. It is unilateral and its location is behind and around eyes.
4. It is excruciating, sharp and steady.
5. Its duration is from 10 minutes to 3 hours.
6. It can cause unilateral sweating, facial flushing, nasal congestion and lacrimation.

Characteristics of Tension Type headache:
1. It is more often in females than in males.
2. It occurs usually under stress.
3. It is bilateral in band around head.
4. It is dull and persistant.
5. It occurs in episodes from 30 minutes to 7 days and.
6. It can cause mild intolerance to light and noise.

Tension type headaches respond very well to over the counter analgesics.

Characteristics of Migraine:
1. It occurs in females more often than males.
2. It is variable and can start any time.
3. It is unilateral.
4. The pain caused by this is pulsating and throbbing.
5. It can last, in episodes, from 2 to 72 hours.
6. It can cause visual auras, sensitivity to light and sound, pale facial appearance, nausea and vomiting.

Types of Migraine headache:

Note: Migraine and cluster headaches are the types of “Vascular headaches”, whereas Tension headache is the most common form of “Myogenic / Muscular headache”.

Biologic basis of Migraine Headache:
Hypoperfusion occurs in Migraine with aura. Migranious aura is due to abnormally high release of serotonin from platelets.

Firstly: There is a spreading depression of neuronal activity.
Secondly: Reduced blood flow in the most posterior part of the cerebral hemisphere.
Thirdly: This hypoperfusion spreads on the surface of the cortex.

These hypoperfused regions show an abnormal response to changes in arterial pCO2 (this is alteration of function) and there is an increase in the amplitude of temporal artery pulsations.

Hypoperfused state remains during aura and headache phase and after that hyperperfused state comes.

No hypoperfusion occurs in Migraine without aura.

Pain in migraine headaches is considered to be due to extra cranial and intracranial arterial dilation that results in release of neuro-active molecules such as substance P.

In woman, whose headache is related to menstrual cycle, migraine is due to
1. Falling levels of estrogen.
2. Elevated levels of prostaglandin E1.

Phases in Migraine headache:
There are three phases:
1. Asymptomatic phase: No symptoms or pathologic features are found between the previous attack and until next attack.
2. Prodromal Phase: It starts with visual disturbances. In this phase there is vasoconstriction of arteries and release of serotonin.
3. Headache Phase: Here pain starts along with nausea and vomiting. Here, cerebral vasodilation occurs and due to release of serotonin, there is a large amount of serotonin.

Treatment of Migraine:

Prophylaxis of Migraine headache:
When there is recurrence of migraine headache two or more times in a month. Drugs on prophylactic bases can be taken such as β-blockers (propranolol, nadolol) can be taken. Some ergot alkaloids like Methysergide are also effective.

Acute migraine headache:
When the first symptoms of migraine headache started, following medicines are effective to prevent the near future headache:
1. Sumatriptan
2. Ergotamine
3. Dihydroergotamine

Prastaglandins

We will study Prostaglandins only in Eicosanoids . Prostaglandins are unsaturated fatty acids found in almost all mammals and have the activity very closely to the hormones such as controlling smooth muscle contraction, blood pressure, inflammation and body temperature.


They contain cyclic ring structure made with the help of 20 carbon atoms.

Prostaglandins act on the tissues in which they are synthesized and within no time metabolized to useless products at the site of action.

Synthesis of Prostaglandins and Leukotrienes:

Action:
Prostaglandins bind to various membrane receptors via G-proteins, subsequently resulting in the activation or inhibition of adenylyl cyclase or stimulate phospholipase C. This causes an enhanced formation of diacylglycerol and IP3.

PGF2α, leukotrienes and thromboxane A2 mediate certain actions by:
1. Activating phosphatidylinositol metabolism.
2. Causing an increase of intracellular Ca2+.

Functions:
These are released in allergic and inflammatory processes. They act as local signals and very specifically. They functions vary widely among the tissues. For example, TXA2 triggers contraction in certain smooth muscles while their release from platelets triggers the recruitment of new platelets for aggregation.

Therapeutic Uses:
1. Abortion (Dinoprost, dinoprostone, carboprost, misoprostol alongwith methotrexate in terminating pregnancy in the 1st trimester).
2. Peptic Ulcers (misoprostol, a synthetic PGE1, is used to inhibit the secretion of HCL in stomach).
3. Alprostadil (PGE1), A vasodilator used for palliative therapy (treating symptoms only) to temporarily maintain patency of the ductus arteriosus (a fetal vessel in the 1st two months after birth) in neonates with congenital heart defects.
4. Dinoprost (PGF2α), It is used as an oxytocic agent (A drug that speeds up the child birth).
5. Dinoprostone (PGE2), An oxytocic agent used as an abortifacient.

Metabolism:
Prostaglandins are rapidly catabolized in the body by:
1. 15-Hydroxydehydrogenase pathway.
2. Cytochrome P450 system.

Histamine

A depressor amine (as it causes lowering of the blood pressure). It is derived from histidine (as shown below) and is also present in ergot and animal tissues.
Synthesis:

Storage:

It is stored in most tissues in
(1) mast cells and in blood, in
(2) basophil. Histamine is stored in their secretary granules.
It is also present in
(3) cells of the epidermis,
(4) cells in the gastric mucosa,
(5) neurons in the central nervous system and
(6) cells in regenerating or rapidly growing tissues.

Release of Histamine:
Histamine is released by the process of exocytosis. This is stimulated
1. Either by the interaction of complement components C3a and C5a with specific receptors on the cell surface or
2. Interaction of antigen with cell fixed IgE antibodies.

This secretion of histamine is initiated by Ca2+.

Some drugs like morphine and tubocurarine, release histamine by some non-receptor action.

Metabolism:

Metabolized by
1. Histaminase
2. Methylating enzyme “Imidazole N. Methyltransferase” which converts this into methylhistamine.

Histamine receptors:
Following are the histamine receptors and the table shown below is giving an overview histamine receptors:

Clinical Uses of Histamine agonists:
1. As a provocative test of bronchial asthma hyperactivity.
2. As a diagnostic agent in testing for gastric acid secreting ability.

Histamine antagonists:

Mechanism of action of Histamine antagonists:
They block the action of histamine receptors at all level.

Generations of H1 receptor blocking agents:
There are two generations of H1 receptor blocking agents:

1st generation:

Key Members

• Diphenhydramine
• Chlorpheniramine
• Doxylamine
• Hydroxyzine

Characteristics
• High lipophilicity, easily enters CNS
• Highly sedative (Triprolidine, Promethazine, Hydroxyzine)
• Anti-muscarinic, anti-α-adrenergic, anti-5HT
• Some have anti-motion sickness effect (Dimenhydrinate)
• Some have local anaesthetic effect.
• May cause increase appetite and weight gain. (Cyproheptadine)

2nd generation:

Key Members
• Desloratadine (loratadine)
• Fexofenadine (terfenadine)
• Cetirizine
• Azelastine
• Astemazole

Characteristics
• No CNS entry (Low lipophilicity, most ionized; also protein binding)
• Non-sedating
• No significant autonomic receptor blocking effect
• Generally long-acting
• Some are cardiotoxic
• May cause anorexia. (Loratidine)

Pharmacokinetics:
1. Orally they are well absorbed with maximum serum levels occur after 1-2 hours.
2. Average plasma T1/2 is 4-6 hours.
3. H1 receptor blockers distribute to all the tissues.
4. Biotransformation is mainly in the liver.
5. Excreted in the urine.

Clinical uses of H1 receptor antagonists:
1. Allergic conditions.
2. Motion sickness and nausea.
3. Somnifacients. Diphenhydramine can be used for the treatment of insomnia.

Clinical uses of H2 receptor antagonists:
1. In the treatment of ulcers.
2. Treatment of Zollinger-Ellison syndrome (severe hypersecretion and ulceration).
3. Gastro-esophageal reflux disease (GERD).

Adverse effects:
Sedation, Headache, Flushing, tachycardia, Diarrhea, Cause itching and pain.

Autacoids

Autacoids are local biological factors which act like local hormones.

Speciality:

1. They have a short life time.
2. They act near their site of synthesis.

These things are differentiating them from other hormones and neurotransmitters.

Cough

It is the process of releasing air through the windpipe and mouth in a sudden noisy manner. Cough is initiated when there is a mechanical or chemical irritation to bronchi and trachea or by pressure from adjacent structures. Larynx and carina are especially sensitive to chemical stimuli such as SO₂ gas or chlorine gas.

Useful aspects of cough:
It is a physiological mechanism which:
1. Clears the respiratory pathways from foreign materials and extra secretions
2. May help to prevent sudden collapse of lungs.

Tuberculosis

Symptoms of tuberculosis:


Early symptoms:
Usually no symptoms develop but sometimes influenza is present.

Symptoms in second stage:
1. Low fever
2. Weight loss
3. Chronic fatigue
4. Heavy sweating especially at night

Later stages:
1. Cough with sputum that becomes progressively bloody, yellow, thick or grey
2. Chest pain
3. Shortness of breath
4. Reddish or cloudy urine

Hypertension

It is an arterial disease accompanied by abnormally high blood pressure. It is also called as “Hyperpiesis” or “Hyperpiesia”.

Systolic pressure:

Persistent systolic blood pressure at about 140 mmHg or greater

Diastolic pressure:
Persistent diastolic blood pressure at about 90 mmHg to 110 mmHg

After effects of hypertension:
1. Congestive cardiac failure
2. Myocardial infarction
3. Renal damage
4. Other cerebrovascular disorders.

Vomiting

It is the forcible throwing of contents of stomach up through mouth as a result of involuntary spasms of the muscles of the stomach. It is also called emesis.
The chemoreceptor trigger zone as well as vomiting center of the medulla oblongata is involved in the emesis.

Following illustration is helpful in this context.

Causes of vomiting:

Vomiting may have from one of the following causes:

1. Motion sickness
2. Intestinal obstruction
3. Disease or disorder of the inner ear
4. Some kind of injury to the head
5. Appendicitis
6. Adverse effects or direct effects of certain drugs
7. Pregnancy
8. Renal failure

After effects of vomiting:
In severe cases vomiting may result in dehydration, malnutrition, or rupturing of the esophageal wall.

Therapeutic strategies:
Its treatment is directly towards the cause or origin of vomiting. It is beneficial to drink a lot of clear water or any other fluids so that the chances of dehydration will not be there.

On the other hand, medicines can also be used.

Nausea

It is the disturbance of the stomach which accompanies the feeling to vomit.

Nausea directly is caused from irritation of the nerve endings present in the stomach or duodenum, which stimulates nausea and vomiting control centers present in the brain.

Causes of nausea:
The most common causes of nausea are
1. Indigestion:
The nausea caused by indigestion is due to eating too rapidly or emotional stress.

2. Motion sickness:
This is caused by the disturbance in the balance organs of the inner ear i.e. semicircular canals of the ear. The messages for disturbance go to the lower brain.

3. Pregnancy:

Natural anti-coagulants present in the body

These are of the following types:

1. Those that causes inhibition of fibrin (Fibrin Inhibitors)
These are basically inhibitors of protease. They causes the inhibition of coagulation proteins as they move from the site of vessel injury.

2. Those that causes lysis of fibrin (Fibrinolytics)
These are basically tissue plasminogen activators.

Hemostasis

It refers to the spontaneous arrest of the flow of blood from a vessel which is damaged.
Hemostatic response:
Vasospasm:
Vessels become spasmodic suddenly after the vessel is damaged.

Formation of platelet plug:
After the endothelium is damaged the platelets get stick to collagen as well as to each other resulting in the formation of platelet plug.

Several factors are released by platelets such as ADP, TXA2, and serotonin which results in further aggregation of platelets as well as vasoconstriction.

Next in the process, aggregated plug of platelets make it possible for the platelet factor 3 availability leading to the sequence of coagulation process further to take place.

Fibrin reinforcement of platelet plug:
A series of reactions are activated after the stimulation of coagulation system. Coagulation system works through two interrelated processes – Intrinsic and extrinsic processes.

Extrinsic pathway:
Extrinsic denotes something that comes from outside. Extrinsic pathway denotes a series of reactions which is activated by tissue factor that comes from outside of blood.

It activates Factor VII by a tissue factor i.e. thromboplastin

Intrinsic Pathway:
Intrinsic denotes something which is found in body part. In the intrinsic pathway proteins for the activation of the process of blood coagulation are present in the blood.
Intrinsic process activates Factor XII.
Both of these processes mainly activate the formation of thrombin.
And in the final result fibrin molecules are released which are helpful for giving firmness to the platelet plug.

Memory

Memory represents the efficiency of the mind to keep the aquired information and knowledge of the previous occasions and to restore it.

Types of memory:
1. Short term memory
2. Long term memory

Digestive System 3 (Objective Type Questions)

Functional Types of movements in the GIT:


32. The basic propulsive movement of the GIT tract is called ..........................

33. The usual stimulus for intestinal peristalsis is called ...............................

34. peristalsis is stimulated by :

a) chemical stimulus

b) physical stimulus

c) parasympathetic nervous signals

d) Both a&b

e) only c

f) all of above

35. Mixing movements are ................................. in different parts of the elementary tract.

a) remain same

b) changed variously

c) rhythmic

36. Peristalsis occurs only weakly or not at all in any potion of the GIYY tract that has congenital absence of the ………………

37. The direction of the peristalsis can be :

a) unidirectional

b) bidirectional

c) only towards anus

d) a & c

38. When a segment of the intestinal tract is excited by distention and thereby initiates peristalsis ,the contractile ring causing the peristalsis normally begins on the orad side and travels towards :

a) from distended segment to the extended segment

b ) from extended segment to the distended segment

c) towards distended segment only

39. IN some areas ,the peristaltic contractions themselves cause most of the mixing .This is true about ………………….

40. The blood vessels of the GIT are part of a more extensive system called the ………………..

41. The vein which carries the blood through the spleen , pancreas , and gut is called ……………..

42. Semisolid mixture of the food with the gastric secretions is called as……………….

43. Anatomically ,the stomach is usually devided into two major parts named as…………&…………

44. Saliva secretions contain two types of proteins which are: a) mucin and lysine

b) albumin and ptyalin

c) histidine and thymine

d) mucin and ptyalin

45. A typical stomach oxyntic gland is composed of three types of cells i.e.mucous neck cells , peptic cells & ………………

46. Protein digesting enzymes secreted by pancrease gland are: ………………………………………………..

47. The two important component of the pancreatic juice i.e. bicarbonate ions & water are secreted by:

a) acini

b) epithelial cells of the ductules and ducts

c) iselet cells of the pancrease

d) both a& b

48. End product of the hemoglobin is called as…………….

49. Bilirubin & cholesterol is excreated from the body as waste product in the form of ……………….

50. Brunner’s gland is located in the wall of the :

a) jejunum

b) ileum

c) duodenum ,

d) scrotum

Answers to Objective Type Question of Digestive System:

32. peristalsis


33. distention of the gut

34. f

35. b

36. myenteric plexus

37. d

38. c

39. sphincters

40. splanchnic circulation

41. portal vein

42. chime

43. body and antrum

44. d

45. parietal cells

46. trypsin, chymotripsin and carboxypolypeptidase

47. b

48. bilirubin

49. bilirubin

50. c

Further Reading:
Textbook of Medical Physiology: With STUDENT CONSULT Online Access

Guyton and Hall Physiology Review

Pocket Companion to Guyton & Hall Textbook of Medical Physiology

Tag:
Multiple Choice Questions, Pharmacy, Physiology, Medical, Pharmacist, Doctor

Digestive System 2 (Objective Type Questions)

Neuronal control of GIT function enteric nervous system :


20. The nervous system of the GIT is called as ............................

21. The number of neurons in enteric nervous system is is about 100 million which is assumed to be aqual to the number in the..........................

22. The outer plexus of enteric nervous system lies b/w the ........................and ...................... layers called myenteric plexuses.

23. sub mucosal plexuses of the enteric nervous system is called as...................,that lies in the sub mucosa.

a) myenteric plexus,

b) Meissner's plexus

c) none of the above

24. The GIT movements are controlled by ;

a) sub mucosal plexus

b) myenteric plexus

c) hormonal secretions

25. GIT secretions and local blood flow is controlled by :

a) sub mucosal plexus

b) myenteric plexus

c) hormonal secretions

Differences b/w the Myenteric and submucosal plexuses:

26. My enteric plexus consists of a ..................chain of interconnected neurons that extends the entire length of the gastrointestinal tract.

a) circular

b) branched

c) linear

27. what is wrong about the GIT smooth muscle stimulation :

a) Stimulation of My enteric plexus causes the decreased tonic contraction .

b) Stimulation of My enteric plexus causes the increased rate of rhymes of contraction .

c) Stimulation of My enteric plexus causes the decreased intensity of chemical contractions .

d) Stimulation of My enteric plexus causes the increased velocity of inhibition of the excitatory waves along the gut wall.

28. Myenteric plexus are :

a) excitatory ,

b) inhibitory

c) not completely inhibitory

d ) not completely excitatory

29. The inhibitory neurotransmitter secreted by my enteric plexus is called ..............................

30. Control of function within the inner wall of each minute segment is handled by .....................

a) hormonal secretions

b) myenteric plexus

c) sub mucosal plexus ,

d) non of the above

Types of Neurotransmitters Secreted by Enteric Neurons:

31. About more than 12 types of neurotransmitters are secreted by enteric neurons ,out of which more familiar are:

a) cholecystokinin

b) adenosine triphosphate

c) serotonin

d) Acetylcholine and epinephrine.

Answers to Objective Type Questions of Digestive System:

20. enteric nervous system .


21. spinal cord.

22. longitudinal ,circular

23. b

24. b

25. a

26. c

27. b

28. d

29. intestinal polypeptide

30. ()

31. d

Further Reading:
Textbook of Medical Physiology: With STUDENT CONSULT Online Access
Guyton and Hall Physiology Review

Pocket Companion to Guyton & Hall Textbook of Medical Physiology
 
Tag:
Preparation of Pharmacy Exams, Tests of Physiology, MCQs of Physiology

Digestive System 1(Objectives)

General principles of Gastrointestinal Functions :

1. The alimentary tract provides the body with:

a) water and electrolytes

b) nutrients

c) enzymes

d) Both a & b

2. The GIT tract consists of the layers;serosa ,longitudinal muscle layer ,circular muscle layer, submucosa and ......................

3. The motor functions of gut are performed by ;

a) smooth muscle layer

b) circular muscle layer

c) serosa

d) both a&b

GIT SMOOTH MUSCLES FUNCTIONS:

4. An individual smooth muscle is ....................micrometer in length and .............................micrometer in diameter.

5. The peristalsis is regulated by two main types of muscles i.e.: .....................................................

6. The active potential of muscles is stored in the form of : .................................

Electrical activity of GIT smooth muscles:

7. The smooth muscle of the GIT is excited by continual electrical activity which is :

a) slow

b) fast

c) slow and intrinsic

d) fast and intrinsic

8. The motor activity of GIT is controlled mainly by :

a) neuronal control

b) change in resting membrane potential

c) hormonal secretions

d) both a&b

9. Most gastrointestinal contractions occur rhythmically and this rhythm is determined mainly by the frequency of the ................................. of smooth muscles .

10. slow waves are undulating changes in resting membrane potential and its intentisity varies b/w 5-15 .......................

11. It is assumed that the electrical pacemaker of the smooth muscle cells are ........................

12. The muscle contraction is excited by :

a) spike potential

b) slow waves

c) neuronal and hormonal stimulation

13. The true Action potential of smooth muscles of GIT is called as .................................

14. The important difference b/w Action potential of GIT smooth muscles and nerve fiber is ...................

15. The duration of action potential of smooth muscle fibers of GIT is .....................than that of neuron fibers . a) less

b) long

c) much more

d) much less

16. When resting membrane potential becomes more negative ,the smooth muscle fibers of GIT become more .................

17. Acetylcholine causes the smooth muscles to be ..........................

a) polarized ,

b) depolarized ,

c) make more excitable

d) make less excitable

18. Parasympathetic nerve stimulation causes the ................................... of the smooth muscles of GIT .

19. Epinephrine & nor-epinephrine cause the ...................................of the smooth muscles of GIT .

Answers to Objective Type Questions of Digestive System:

1. d


2. mucosa

3. a

4. 200 to 500 and 2 to 10

5. longitudinal and circular

6. Na & Cl ions

7. c

8. b

9. Slow waves.

10. Milli volts

11. interstitial cells .

12. a

13. spike potential

14. manner of generation

15. b

16. excitable

17. b

18. excitable

19. hyper polarization/ less excitation

Further Reading:
Textbook of Medical Physiology: With STUDENT CONSULT Online Access

Guyton and Hall Physiology Review

Pocket Companion to Guyton & Hall Textbook of Medical Physiology

Tag:
Preparation of Pharmacy Exams, Tests of Physiology, MCQs of Physiology

Skin

(This topic has been written by a student from Hajvery University, Lahore)
The skin is the largest organ of the body and has a surface area of about 1.5 to 2m2 in adults and it contains glands, hairs and nails. The skin completely covers the body and is continuous with the membranes lining the body orifices.


Structure of the skin

Structurally skin is divided into following layers:

1. Epidermis
2. Dermis

Between the skin and underlying structures is a subcutaneous layer of fat.

Epidermis:

Most superficial layer of the skin is epidermis and is composed of stratified keratinized squamous epithelium which varies in thickness in different parts of the body. It is thickest in the palms of the hands and soles of the feet. There are no blood vessels or nerve endings in the epidermis, but its deeper layers are bathed in interstitial fluid from the dermis, which provides oxygen and nutrients, and is drained away as lymph. There are several layers of cells in the epidemic which extend from the deepest germinative layer to the surface stratum corneum which is thickest Horney layer. The cells on the surface are flat, thin, non-nucleated, dead cells, or squamis, inwhich the cytoplasm has been replaces by the fibrous protein keratin. These cells that originated in the germinative layer and have undergone gradual change as they progressed towards the surface. Complete replacement of the epidermis takes about a month. The maintenance of the healthy epidermis depends upon three processes being synchronized:

• desquamation (shedding ) of the keratinized cells form the surface

• effective keratinisation of the cells approaching the surface

• Continual cell division in the deeper layers with newly formed cells being pushed to the surface.

Hairs, secretions from sebaceous glands and ducts of sweat glands pass through the epidermis to reach the surface .The surface of the epidermis is ridged by projections of cells in the dermis called papillae. The pattern of ridges is different in every individual and the impression made by them is the 'fingerprint’. The downward projections of the terminative layer b.w the papillae are believed to aid nutrition of epidermal cells and stabilize the two layers, prevention damage due to shearing forces. Blisters and epidermis and serous fluid collects b/w the two layers.

Color of the skin

Various factors affect the color of the skin; some of these factors are as following;

• Melanin :It is a dark pigment derived from the amino acid tyrosine and secreted by melanocytes in the deep germinatve layer , is absorbed by surrounding epithelial cells .The amount is genetically determined and varies b/different parts of the body, b/w people of the seem ethnic origin and b/w ethnic groups. The number of melanocytes is fairly constant so the differences in color depends on the amount of melanin secreted It protects the skin from the harmful effects of sunlignt.Exposure to sunlight promotes synthesis of melanin.

• The percentage saturation of heaemoglobin and the amount of blood circulating in the dermis give white skin white skin its pink color.

Excessive levels of bile pigments in blood and carotenes in subcutaneous fat give the skin a yellowish colour.

Dermis

The dermis is tough and elastic .It is formed from connective tissue and the matrix contains collagen fibers interlaced with elastic fibres.Rupture of elastic fibers occurs when the skin is overstretched, resulting in permanent striate ,or stretch marks, that may be found in pregnancy and obesity. Collagen fibers bind water and give the skin its tensile strength, but as this ability declines with age, wrinkles develop. Fibroblasts, macrophages and mast cells ate the main cells found in the dermis .Underlying its deepest layer there is areola tissue and varying amounts of adipose tissues. The structures in the dermis are:

• blood Bessel

• lymph vessels

• sensory nerve endings

• sweat glands and their ducts

• Hairs, arrector pili muscles and sebaceous glands.

Blood vessels

Arterioles from a fine network with capillary branches supplying sweat glands, sebaceous glands, hair follicles and the dermis .The epidermis has no blood supply. It obtains nutrients and oxygen from interstitial fluid derived from blood vessels I the papilles of the dermis.

Lymph vessels

These form a network throughout the dermis.

Sensory nerve endings

Sensory receptors (specialized nerve endings) sensitive to touch, temperature, pressure, and pain are widely distributed in the dermis .Incoming stimuli activate deferent types of sensory receptors through which individuals receive unformation about their environment. Nerve impulses, generated in the sensory receptors in the dermis, are conveyed to the apical cord by sensory nerves, then to the sensory area of the cerebrum where the sensations are perceived.

Sweat glands

These are widely dies tribute throughout the skin and are most numerous in the palms of the hands, soles of the feet, axillae and groins. They are composed of epithelial cells. The bodies of the glands lie coiled in the subcutaneous tissue. Some ducts open onto the skin surface at tiny depressions, or pores, and others open into hair follicles. Glands opening into hair follicles do not become active until puberty. IN the maxilla they secrete odourless milky fluids which, if decomposed by surface microbes, caudles unpleasant odour .The functions of this secretion are not known. Sweat glands are stimulated by sympathetic nerves in response to raised body temperature and fear. The most wanted and important function of sweat secreted by glands opening onto the skin surface is in the regulation of body temperature. Evaporation of sweat from body surface takes heat from the body core and the amount of sweat produced is governed by the temperature -regulating centre in the hyppothalamus.Excessive sweating may lead to dehydration and serious depletion o f sodium chloride unless intake of water and salt is appropriately increased .After 7 to 10 days exposure to high environmental temperatures the amount of salt lost is substantially reduced but water loss remains high.

Hairs

These are formed by a down -growth of epidermal cells into the dermis or subcutaneous tissue, called hair follicles. At the base of the follicle is a cluster of cells called the bulb? The hair is formed by multiplication of cells of the bulb and as they are pushed upwards, away from their source of nutrition, the cells die and become keratinized .The part of the hair above the skin are the shaft and the remainder, the root. The color of the hair is genetically determined and depends on the amount of melanin present. White hair is the result of the replacement of melanin by tiny air bubbles.

The arrestor pile

These are little bundles of smooth muscles fibers attached to the hair follicles .Contraction makes the hair stand erect and raises the skin around the hair, causing 'goose flesh'.Teh muscles are stimulated by sympathetic neurone fibers in response to fear and cold. Erect hairs trap air, which acts as an insulating layer. This is an efficient warming machine especially when accompanied by shivering, i.e. involuntary contraction of skeletal muscles.

The sebaceous glands

These consist of secretary epithelial cells derived from the same tissue as the hair follicles .they secrete an oily substance, sebum, into the hair follicles and are present in the skin of all parts of the body except the palms of the hands and the soles of the feet. They are most numerous in the skin of the scalp, face, axillae,and groins. In regions of transition from one type of superficial epithelium to another, such as lips, eyelids, nipple, labiaminora, and glens penis, there are sebaceous glands that are independent of hair follicles, secreting sebum directly onto the surface. Sebum keeps the hair soft and pliable and gives it a shiny appearance. On the skin it provides some water-proofing and acts as a bactericidal and fungicidal agent, preventing infection. It also prevents drying and cracking of skin, especially on exposure to heat and sunshine .The activity of these glands increases at puberty and is less at the extremes of age, rendering infants and older adults prone to the effects of excessive moisture.

Nails

Human nails are equivalent to the claws, houns and hoofs of animals. They are derived from the same cells as epidermis and hair and consist of hard, honey keratin plates. They protect the tips of the fingers and toes. The root of the nail is embedded in the skin is covered by the cuticle and forms the hemispherical pale area called the lunula.The nail plate is the exposed partthat has grown out from the terminative zone of the epidermis called the nail bed.Fingernails grow mire quickly than toe nails and growths quicker when the environmental temperature is high.

Functions

Protection: The s of skin kin forms a relatively waterproof layer, provided mainly by its keratinized epithelium, which protects the deeper and more delicate structures .As an important non-specific defense mechanism it acts as a barrier against;

• Invasion by microbes

• Chemicals

• Physical agents, e.g. mild trauma, U.V light

• Dehydration

The epidermis contains specialized immune cells called Algerians cells .They phagocytes intruding antigens and travel to lymphoid tissue, where they present antigen to T-lymphocytes, thus stimulating an immune response.

Due to the presence of the sensory nerve endings in the skin the body reacts by reflex action to unpleasant or painful stimuli, protecting it from further injury .The pigment melanin affords some protection against harmful U.B rays in sunlight.

Regulation of body temperature

The temperature of the body remains fairly constant at about 36.8 across a wide range of environmental temperature .In health, variations ate usually limited to b/w 0.5 and 0.75 although it is raised slightly in the evening, during exercise and in women just after ovulation .When metabolic rate in creases ,body temperature rises, and when it decreases body temperature falls .To ensure this constant temperature ,a balance is maintained b/3 heat produced in the body and heat lost to the environment .

Heat production

Some of the energy released in the cells during metabolic activity is in the form of heat and the must active organs produce the most heat .The principal organ s involved are as follows:

• The muscles: contraction of skeletal muscles produces a large amount of heat and the more strenuous the muscular exercise, the grater the heat produced .Shivering also involves skeletal muscles contraction and produces heat when there is the risk of the body temperature falling below normal.

• The liver is very metabolically active, and heat is produced as a by-product .Metabolic rate and heat production is increased after eating.

• The digestive organs produce heat during peristalsis and during the chemical reaction involved in digestion.

Heat loss

Most heat loss from the body occurs through the skin .Small amounts are lost in expired air, urine and faces .Only heat loss through skin can be regulated; there is no control over heat lost by the other routes .Heat loss through the skin is affected by the difference b.w body and environmental temperatures, the amount of the body surface exposed to the air and the type of clothes worn. Air is a poor conductor of heat and when layers of air are trapped in clothing and b/w the skin and clothing they act as effective insulators against excessive heat loss. For this reason several layers of lightweight clothes provide more effective insulation against a low environmental temperature than one heavy garment. A balance is maintained b.w heat production and heat loss.

Mechanisms of heat loss

In evaporation, the body is cooled when heat is used to convert the water in sweat to water vapour. In radiation, exposed parts of the body radiate heat away from the body .In conduction, clothes and other objects in contact with the skin take up heat. In convection, air passing over the exposed parts of the body is heated and rises, cool air replaces it and convection currents are set up. Heat is also lo9st from the clothes by convection.

Control of body temperature

Nervous control: the temperature regulating centre in the hypothalamus is responsive to the temperature of circulating blood. This centre controls body temperature through autonomic nerve stimulation of the sweat gland when body temperature rises. The vasomotor centre in the medulla oblongata controls the diameter of the small arteries and arterioles, and therefore the amount of blood which circulates in the capillaries in the dermis. The vasomotor centre is influence4d by the temperature of its blood supply and by temperature rises, the skin capillaries dilate and the extra blood near the surface increases heat loss by radiation, conduction and convection .The skin is warm and pond in colour .When body temperature falls arteriolar constriction conserves heat and the skin is whiter and feels cool.

Formation of Vitamin – D: 7-dehydrocholesterol is a lipid based substance in the skin, and ultraviolet light from the sun converts it to vitamin D. This circulates into e blood and is used, with calcium and phosphate, in the formation and maintenance of bone.

Coetaneous sensation: sensory receptors consist t of nerve endings in the dermis that are sensitive to touch, pressure, temperature of pain. Stimulation generates nerve impulses in sensory nerves that transmitted to the cerebral cortex. Some areas have more sensory receptors than others causing them to be especially sensitive, e.g. the lips and fingertips.

Absorption

This property is limited but substances that can be absorbed include:

• Some drugs, in transdermal patches, e.g. hormone replacement therapy during the menopause, nicotine as an aid to stopping smoking.

• Some toxic chemicals e.g. mercury.

Excretion

The skin is a minor excretory organ for some substances including:

• Sodium chloride in sweat; excess sweating may lead to low blood sodium levels

• Urea, especially when kidney function is impaired

• Aromatic substances, e.g. garlic and other spices.

Wound healing

The important function of the skin is quick healing of wounds to save the human body from different diseases.


Reference:
Ross and Wilson Anatomy and Physiology in Health and Illness

Physiology: with STUDENT CONSULT Online Access (Costanzo Physiology)

Textbook of Medical Physiology: With STUDENT CONSULT Online Access

Physiology Coloring Book, The (2nd Edition)

Human Physiology
(These are helpful in the preparation of "The Skin" in Physiology)