Gonadotropin-releasing hormone (GnRH)

GnRH is a peptide of 10 amino acids. Its secretion at the onset of puberty triggers sexual development.

Primary Effects

FSH and LH Relaese

Secondary Effects

Increases estrogen and progesterone (in females)

testosterone Relaese (in males)

Growth hormone-releasing hormone (GHRH)

GHRH is a mixture of two peptides, one containing 40 amino acids, the other 44.  GHRH stimulates cells in the anterior lobe of the pituitary to secrete growth hormone (GH).

Corticotropin-releasing hormone (CRH)

CRH is a peptide of 41 amino acids. Its acts on cells in the anterior lobe of the pituitary to release adrenocorticotropic hormone (ACTH) CRH is also synthesized by the placenta and seems to determine the duration of pregnancy.  It may also play a role in keeping the T cells of the mother from mounting an immune attack against the fetus

Somatostatin

Somatostatin is a mixture of two peptides, one of 14 amino acids, the other of 28. Somatostatin acts on the anterior lobe of the pituitary to

• inhibit the release of growth hormone (GH)
• inhibit the release of thyroid-stimulating hormone (TSH)

Somatostatin is also secreted by cells in the pancreas and in the intestine where it inhibits the secretion of a variety of other hormones.

Antidiuretic hormone (ADH) and Oxytocin

These peptides are released from the posterior lobe of the pituitary

Exchange of gases takes place in Lungs

• A person with an average ventilation rate of 7.5 L/min will breathe in and out 10,800 liters of gas each day
• From this gas the person will take in about 420 liters of oxygen (19 moles/day) and will give out about 340 liters of carbon dioxide (15 moles/day)
• The ratio of CO₂ expired/O₂ inspired is called the respiratory quotient (RQ)
  • RQ = CO₂ out/O₂ in = 340/420 = 0.81
  • In cellular respiration of glucose CO₂ out = O₂ in; RQ = 1
  • The overall RQ is less than 1 because our diet is a mixture of carbohydrates and fat; the RQ for metabolizing fat is only 0.7
• All of the exchange of gas takes place in the lungs
• The lungs also give off large amounts of heat and water vapor

Heart is a hollow muscular organ , that is located in the middle mediastinum  between the two bony structures of the sternum and the vertebral column ( a very important location for applying Cardiopulmonary Resuscitation - CPR- ) .
It has a shape of clenched fist , which weighs about 300 grams ( with mild variation between male and female ).
  Heart has an apex that is anteriorly , inferiorly , and leftward oriented , and a base , that is posteriorly , superiorly and rightward oriented   .
 In addition to its apex and base the heart has anterior , posterior and left surfaces.
 
 The wall of the heart is composed of three layers :
 
1. Endocardium : The innermost layer , which lines the heart chambers and is in direct contact with the blood . It is composed of endothelial cells that are similar to those , that line the blood vessels , and of connective tissue too. 
 Endocardium has a smooth surface that prevents blood clotting, as it ensures laminar blood flow .

 Clinical Physiology 
 Endocarditis is the inflammation of the endocardium , which is resistant to antibiotic treatment and difficult to cure.Endocarditis usually involves heart valves and chordae tendineae too.

 2. Myocardium  : The middle layer of the cardiac wall . It is the thickest among the three layers , and is composed of two types of cardiac muscles :
a. contractile muscle cells (form about 98-99% of the cardiac muscle ) .
 b- non-contractile muscle cells ( form about 1-2 % of the cardiac muscles and are the cells that form excitatory-conductive system of the heart).
 The cardiac muscle cells are similar to the skeletal muscles in that they are striated , but similar to the smooth muscles in being involuntary and connected to each others via gap junctions , that facilitate conduction of electrical potential from one cell to the others. Desmosomes adhere cardiac muscle cells to each others .

 3- Epicardium :  is the outermost and protective layer of the heart . It is composed of connective tissue , and form the inner layer of the pericardium ( visceral pericardium - see bellow).

 Pericardium: 
The heart is surrounded by a fluid-fill sac , which is known as pericardium . Pericardium is composed of two layers ( doubled layer membrane ) , between which a fluid-fill pericardial cavity exist .

 The outer layer is called fibrous pericardium , while the inner layer is called serous pericardium , which is subdivided into parietal pericardium and visceral pericardium . The visceral pericardium is the previously mentioned outermost layer of heart ( epicardium) .
Pericardial sac plays an important role in protection of heart from external hazards and infections , as it fixes the heart and limits its motion. It also prevents excessive dilation of the heart.

Clinical physiology: 

When there is excessive fluid in the pericardial cavity as a result of pericardial effusion , a cardiac tamponade will develop . cardiac tamponade means compression of the heart within the pericardial sac , which will prevent the relaxation of the heart ( heart will not be able to fully expand ) , and thus the circulating blood volume will be decreased (obstructive shock) . This is a life threatening situation which has to be urgently cured by  pericardiocentesis . 

Chambers of the heart : 

Heart has four chambers : two atria and two ventricles . The two right and left atria are separated from the two ventricles by the fibrous skeleton , which involves the right ( tricuspid ) and left ( bicuspid ) valves. Right and left atria are separated from each other by the interatrial  septum .
The two ventricles are separated by the interventricular septum.Interventricular septum is muscular in its lower thick part and fibrous in its upper thin part.
The two atria holds the blood returning from the veins and empty it only in a given right moment into the ventricles. Ventricles pump the blood into the arteries . 

Heart valves : 

There are four valves in the heart : Two atrioventricular valves and two semi-lunar valves:
1. Atrioventricular ( AV ) valves: These valves are found between the atria and ventricles , depending on the number of  the leaflets , the right atrioventricular valve is also called tricuspid valve (has three leaflets ) , while the left one is called bicuspid valve (has two leaflets ) . The shape of the bicuspid valve is similar to the mitre of bishop , so it is also called the mitral valve.
The leaflets of the valves are attached to fibrous threads (composed of collagen fibers ) , known as chordae tendineae , which from their side are attached to papillary muscles in the ventricles. These valves prevent backward flow of blood from ventricles during the systole. 

2. Semi-lunar valves : 

These valves are located on the base of the arteries ( aorta and pulmonary artery ) . They prevent the backward flow of blood from the arteries into ventricles.
The structure of the semilunar valves is quite different from that of the AV valves , as they have crescent-shaped cusps that do not have chorda tendinea , instead these cusps are like pockets which are filled of blood when it returns to the ventricles from the lumen of arteries during the diastole  , so they get closed and prevent the backward flow of blood.

The Nervous System Has Peripheral and Central Units

• The central nervous system (CNS) is the brain and spinal column
• The peripheral nervous system (PNS) consists of nerves outside of the CNS
• There are 31 pairs of spinal nerves (mixed motor & sensory)
• There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)

The pattern of innervation plotted on the skin is called a dermatome

The Nervous System Has Peripheral and Central Units

• The central nervous system (CNS) is the brain and spinal column
• The peripheral nervous system (PNS) consists of nerves outside of the CNS
• There are 31 pairs of spinal nerves (mixed motor & sensory)
• There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)

The pattern of innervation plotted on the skin is called a dermatome

Structure and function of skeletal muscle.

Skeletal muscles have a belly which contains the cells and which attaches by means of tendons or aponeuroses to a bone or other tissue. An aponeurosis is a broad, flat, tendinous attachment, usually along the edge of a muscle. A muscle attaches to an origin and an insertion. The origin is the more fixed attachment, the insertion is the more movable attachment. A muscle acts to shorten, pulling the insertion toward the origin. A muscle can only pull, it cannot push.

Muscles usually come in pairs of antagonistic muscles. The muscle performing the prime movement is the agonist, the opposite acting muscle is the antagonist. When the movement reverses, the names reverse. For example, in flexing the elbow the biceps brachii is the agonist, the triceps brachii is the antagonist. When the movement changes to extension of the elbow, the triceps becomes the agonist and the biceps the antagonist. An antagonist is never totally relaxed. Its function is to provide control and damping of movement by maintaining tone against the agonist. This is called eccentric movement.

Muscles can also act as synergists, working together to perform a movement. This movement can be different from that performed when the muscles work independently. For example, the sternocleidomastoid muscles each rotate the head in a different direction. But as synergists they flex the neck.

Fixators act to keep a part from moving. For example fixators act as postural muscles to keep the spine erect and the leg and vertebral column extended when standing. Fixators such as the rhomboids and levator scapulae keep the scapula from moving during actions such as lifting with the arms.

The Adrenal Glands

The adrenal glands are two small structures situated one at top each kidney. Both in anatomy and in function, they consist of two distinct regions:

• an outer layer, the adrenal cortex, which surrounds
• the adrenal medulla.

The Adrenal Cortex

cells of the adrenal cortex secrete a variety of steroid hormones.

• glucocorticoids (e.g., cortisol)
• mineralocorticoids (e.g., aldosterone)
• androgens (e.g., testosterone)

• Production of all three classes is triggered by the secretion of ACTH from the anterior lobe of the pituitary.

Glucocorticoids

They Effect by raising the level of blood sugar (glucose). One way they do this is by stimulating gluconeogenesis in the liver: the conversion of fat and protein into intermediate metabolites that are ultimately converted into glucose.

The most abundant glucocorticoid is cortisol (also called hydrocortisone).

Cortisol and the other glucocorticoids also have a potent anti-inflammatory effect on the body. They depress the immune response, especially cell-mediated immune responses. 

Mineralocorticoids

The most important of them is the steroid aldosterone. Aldosterone acts on the kidney promoting the reabsorption of sodium ions (Na⁺) into the blood. Water follows the salt and this helps maintain normal blood pressure.

Aldosterone also

• acts on sweat glands to reduce the loss of sodium in perspiration;
• acts on taste cells to increase the sensitivity of the taste buds to sources of sodium.

The secretion of aldosterone is stimulated by:

• a drop in the level of sodium ions in the blood;
• a rise in the level of potassium ions in the blood;
• angiotensin II
• ACTH (as is that of cortisol)

Androgens

The adrenal cortex secretes precursors to androgens such as testosterone.

Excessive production of adrenal androgens can cause premature puberty in young boys.

In females, the adrenal cortex is a major source of androgens. Their hypersecretion may produce a masculine pattern of body hair and cessation of menstruation.

Addison's Disease: Hyposecretion of the adrenal cortices

Addison's disease has many causes, such as

• destruction of the adrenal glands by infection;
• their destruction by an autoimmune attack;
• an inherited mutation in the ACTH receptor on adrenal cells.

Cushing's Syndrome: Excessive levels of glucocorticoids

In Cushing's syndrome, the level of adrenal hormones, especially of the glucocorticoids, is too high.It can be caused by:

• excessive production of ACTH by the anterior lobe of the pituitary;
• excessive production of adrenal hormones themselves (e.g., because of a tumor), or (quite commonly)
• as a result of glucocorticoid therapy for some other disorder such as
  • rheumatoid arthritis or
  • preventing the rejection of an organ transplant.

The Adrenal Medulla

The adrenal medulla consists of masses of neurons that are part of the sympathetic branch of the autonomic nervous system. Instead of releasing their neurotransmitters at a synapse, these neurons release them into the blood. Thus, although part of the nervous system, the adrenal medulla functions as an endocrine gland.The adrenal medulla releases:

• adrenaline (also called epinephrine) and
• noradrenaline (also called norepinephrine)

Both are derived from the amino acid tyrosine.

Release of adrenaline and noradrenaline is triggered by nervous stimulation in response to physical or mental stress. The hormones bind to adrenergic receptors  transmembrane proteins in the plasma membrane of many cell types.

Some of the effects are:

• increase in the rate and strength of the heartbeat resulting in increased blood pressure;
• blood shunted from the skin and viscera to the skeletal muscles, coronary arteries, liver, and brain;
• rise in blood sugar;
• increased metabolic rate;
• bronchi dilate;
• pupils dilate;
• hair stands on end (gooseflesh in humans);
• clotting time of the blood is reduced;
• increased ACTH secretion from the anterior lobe of the pituitary.

All of these effects prepare the body to take immediate and vigorous action.