Oxygen Transport

In adult humans the hemoglobin (Hb) molecule

• consists of four polypeptides:
  • two alpha (α) chains of 141 amino acids and
  • two beta (β) chains of 146 amino acids
• Each of these is attached the prosthetic group heme.
• There is one atom of iron at the center of each heme.
• One molecule of oxygen can bind to each heme.

The reaction is reversible.

• Under the conditions of lower temperature, higher pH, and increased oxygen pressure in the capillaries of the lungs, the reaction proceeds to the right. The purple-red deoxygenated hemoglobin of the venous blood becomes the bright-red oxyhemoglobin of the arterial blood.
• Under the conditions of higher temperature, lower pH, and lower oxygen pressure in the tissues, the reverse reaction is promoted and oxyhemoglobin gives up its oxygen.

The Posterior Lobe

The posterior lobe of the pituitary releases two hormones, both synthesized in the hypothalamus, into the circulation.

• Antidiuretic Hormone (ADH).
  ADH is a peptide of 9 amino acids. It is also known as arginine vasopressin. ADH acts on the collecting ducts of the kidney to facilitate the reabsorption of water into the blood.
  • A deficiency of ADH
    • leads to excessive loss of urine, a condition known as diabetes  nsipidus.
• Oxytocin
  Oxytocin is a peptide of 9 amino acids. Its principal actions are:
  • stimulating contractions of the uterus at the time of birth
  • stimulating release of milk when the baby begins to suckle

Properties of cardiac muscle

Cardiac muscle is a striated muscle like the skeletal muscle , but it is different from the skeletal muscle in being involuntary and syncytial .

Syncytium means that cardiac muscle cells are able to excite and contract together due to the presence of gap junctions between adjacent cardiac cells.

Cardiac muscle has four properties , due to which the heart is able to fulfill its function as a pumping organ. Studying and understanding these properties is essential for students to understand the cardiac physiology as a whole.

1. Rhythmicity ( Chronotropism )
2. Excitability ( Bathmotropism ) 
3. Conductivity
4. Contractility

• There Are 12 Pairs of Cranial Nerves

• The 12 pairs of cranial nerves emerge mainly from the ventral surface of the brain
• Most attach to the medulla, pons or midbrain
• They leave the brain through various fissures and foramina of the skull

• Nerve	Name	Sensory	Motor	Autonomic Parasympathetic
  I	Olfactory	Smell
  II	Optic	Vision
  III	Oculomotor	Proprioception	4 Extrinsic eye muscles	Pupil constriction Accomodation Focusing
  IV	Trochlear	Proprioception	1 Extrinsic eye muscle (Sup.oblique)
  V	Trigeminal	Somatic senses (Face, tongue)	Chewing
  VI	Abducens	Proprioception	1 Extrinsic eye muscle (Lat. rectus)
  VII	Facial	Taste Proprioception	Muscles of facial expression	Salivary glands Tear glands
  VIII	Auditory (Vestibulocochlear)	Hearing, Balance
  IX	Glossopharyngeal	Taste Blood gases	Swallowing Gagging	Salivary glands
  X	Vagus	Blood pressure Blood gases  Taste	Speech Swallowing Gagging	Many visceral organs (heart, gut, lungs)
  XI	Spinal acessory	Proprioception	Neck muscles: Sternocleidomastoid Trapezius
  XII	Hypoglossal	Proprioception	Tongue muscles Speech

   

• Many of the functions that make us distinctly human are controlled by cranial nerves: special senses, facial expression, speech.

• Cranial Nerves Contain Sensory, Motor and Parasympathetic Fibers

   

Concentration versus diluting urine 

Kidney is a major route for eliminating fluid from the body to accomplish water balance. Urine excretion is the last step in urine formation. Everyday both kidneys excrete about 1.5 liters of urine.
Depending on the hydrated status of the body, kidney either excretes concentrated urine ( if the plasma is hypertonic like in dehydrated status ) or diluted urine ( if the plasma is hypotonic) .
This occurs thankful to what is known as countercurrent multiplying system, which functions thankfully to establishing large vertical osmotic gradient .
To understand this system, lets review the following facts:
1. Descending limb of loop of Henle is avidly permeable to water.
2. Ascending limb of loop of Henly is permeable to electrolytes , but impermeable to water. So fluid will not folow electrolytes by osmosis.and thus Ascending limb creates hypertonic interstitium that will attract water from descending limb.
Pumping of electrolytes
3. So: There is a countercurrent flow produced by the close proximity of the two limbs.                   
                                                   
Juxtamedullary nephrons have long loop of Henle that dips deep in the medulla , so the counter-current system is more obvious and the medullary interstitium is always hypertonic . In addition, peritubular capillaries in the medulla are straigh ( vasa recta) in which flow is rapid and rapidly reabsorb water maintaining hypertonic medullary interstitium.

In distal tubules water is diluted. If plasma is hypertonic, this will lead to release of ADH by hypothalamus, which will cause reabsorption of water in collecting tubules and thus excrete concentrated urine.

If plasma is hypotonic ADH will be inhibited and the diluted urine in distal  tubules will be excreted as diluted urine.

Urea  contributes to concentrating and diluting of urine as follows:

Urea is totally filtered and then 50% of filtrated urea will be reabsorbed to the interstitium, this will increase the osmolarity of medullary interstitium ( becomes hypertonic ). Those 50% will be secreted in ascending limb of loop of Henle back to tubular fluid to maintain osmolarity of tubular fluid. 55% of urea in distal nephron will be reabsorbed in collecting ducts back to the interstitium ( under the effect of ADH too) . This urea cycle additionally maintain hypertonic interstitium.

DNA (Deoxyribonucleic acid) - controls cell function via transcription and translation (in other words, by controlling protein synthesis in a cell)

Transcription - DNA is used to produce mRNA

Translation - mRNA then moves from the nucleus into the cytoplasm & is used to produce a protein . requires mRNA, tRNA (transfer RNA), amino acids, & a ribosome

tRNA molecule

• sequence of amino acids in a protein is determined by sequence of codons (mRNA). Codons are 'read' by anticodons of tRNAs & tRNAs then 'deliver' their amino acid.
• Amino acids are linked together by peptide bonds (see diagram to the right)
• As mRNA slides through ribosome, codons are exposed in sequence & appropriate amino acids are delivered by tRNAs. The protein (or polypeptide) thus grows in length as more amino acids are delivered.
• The polypeptide chain then 'folds' in various ways to form a complex three-dimensional protein molecule that will serve either as a structural protein or an enzyme.