NEET MDS Lessons
Physiology
Oxygen Uptake in the Lungs is Increased About 70X by Hemoglobin in the Red Cells
- In the lungs oxygen must enter the blood
- A small amount of oxygen dissolves directly in the serum, but 98.5% of the oxygen is carried by hemoglobin
- All of the hemoglobin is found within the red blood cells (RBCs or erythrocytes)
- The hemoglobin content of the blood is about 15 gm/deciliter (deciliter = 100 mL)
- Red cell count is about 5 million per microliter
Each Hemoglobin Can Bind Four O2 Molecules (100% Saturation)
- Hemoglobin is a protein molecule with 4 protein sub-units (2 alphas and 2 betas)
- Each of the 4 sub-units contains a heme group which gives the protein a red color
- Each heme has an iron atom in the center which can bind an oxygen molecule (O2)
- The 4 hemes in a hemoglobin can carry a maximum of 4 oxygen molecules
- When hemoglobin is saturated with oxygen it has a bright red color; as it loses oxygen it becomes bluish (cyanosis)
The Normal Blood Hematocrit is Just Below 50%
- Blood consists of cells suspended in serum
- More than 99% of the cells in the blood are red blood cells designed to carry oxygen
- 25% of all the cells in the body are RBCs
- The volume percentage of cells in the blood is called the hematocrit
- Normal hematocrits are about 40% for women and 45% for men
At Sea Level the Partial Pressure of O2 is High Enough to Give Nearly 100% Saturation of Hemoglobin
- As the partial pressure of oxygen in the alveoli increases the hemoglobin in the red cells passing through the lungs rises until the hemoglobin is 100% saturated with oxygen
- At 100% saturation each hemoglobin carries 4 O2 molecules
- This is equal to 1.33 mL O2 per gram of hemoglobin
- A person with 15 gm Hb/deciliter can carry:
- Max O2 carriage = 1.33 mL O2/gm X 15 gm/deciliter = 20 mL O2/deciliter
- A plot of % saturation vs pO2 gives an S-shaped "hemoglobin dissociation curve"
- At 100% saturation each hemoglobin binds 4 oxygen molecules
At High Altitudes Hemoglobin Saturation May be Well Below 100%
- At the alveolar pO2 of 105 mm Hg at sea level the hemoglobin will be about 97% saturated, but the saturation will fall at high altitudes
- At 12,000 feet altitude alveolar pO2 will be about 60 mm Hg and the hemoglobin will be 90% saturated
- At 29,000 feet (Mt. Everest) alveolar pO2 is about 24 mm Hg and the hemoglobin will be only 42% saturated
- At very high altitudes most climbers must breath pure oxygen from tanks
- During acclimatization to high altitude the hematocrit can rise to about 60%- this increases the amount of oxygen that can be carried
- Hematocrits above 60% are not useful because the blood viscosity will increase to the point where it impairs circulation
Exchange of gases:
- External respiration:
- exchange of O2 & CO2 between external environment & the cells of the body
- efficient because alveoli and capillaries have very thin walls & are very abundant (your lungs have about 300 million alveoli with a total surface area of about 75 square meters)
- Internal respiration - intracellular use of O2 to make ATP
- occurs by simple diffusion along partial pressure gradients
Lung volumes and capacities:
I. Lung`s volumes
1. Tidal volume (TV) : is the volume of air m which is inspired and expired during one quiet breathing . It equals to 500 ml.
2. Inspiratory reserve volume (IRV) : The volume of air that could be inspired over and beyond the tidal volume. It equals to 3000 ml of air.
3. Expiratory reserve volume (ERV) : A volume of air that could be forcefully expired after the end of quiet tidal volume. It is about 1100 ml of air.
4. Residual volume (RV) : the extra volume of air that may remain in the lung after the forceful expiration . It is about 1200 ml of air.
5. Minute volume : the volume of air that is inspired or expired within one minute. It is equal to multiplying of respiratory rate by tidal volume = 12X500= 6000 ml.
It is in female lesser than that in male.
II. Lung`s capacities :
1. Inspiratory capacity: TV + IRV
2. Vital capacity : TV+IRV+ERV
3. Total lung capacity : TV+IRV+ERV+RV
Events in gastric function:
1) Signals from vagus nerve begin gastric secretion in cephalic phase.
2) Physical contact by food triggers release of pepsinogen and H+ in gastric phase.
3) Muscle contraction churns and liquefies chyme and builds pressure toward pyloric sphincter.
4) Gastrin is released into the blood by cells in the pylorus. Gastrin reinforces the other stimuli and acts as a positive feedback mechanism for secretion and motility.
5) The intestinal phase begins when acid chyme enters the duodenum. First more gastrin secretion causes more acid secretion and motility in the stomach.
6) Low pH inhibits gastrin secretion and causes the release of enterogastrones such as GIP into the blood, and causes the enterogastric reflex. These events stop stomach emptying and allow time for digestion in the duodenum before gastrin release again stimulates the stomach.
Principal heart sounds
1. S1: closure of AV valves;typically auscultated as a single sound
Clinical note: In certain circumstances, S1 may be accentuated. This occurs when the valve leaflets are “slammed” shut in early systole from a greater than normal distance because they have not had time to drift closer together. Three conditions that can result in an accentuated S1 are a shortened PR interval, mild mitral stenosis, and high cardiac-output states or tachycardia.
2. S2: closure of semilunar valves in early diastole , normally “split” during inspiration . S2: best appreciated in the 2nd or 3rd left intercostal space
Clinical note: Paradoxical or “reversed” splitting occurs when S2 splitting occurs with expiration and disappears on inspiration. Moreover, in paradoxical splitting, the pulmonic valve closes before the aortic valve, such that P2 precedes A2. The most common cause is left bundle branch block (LBBB). In LBBB, depolarization of the left ventricle is impaired, resulting in delayed left ventricular contraction and aortic valve closure.
3. S3: ventricular gallop, presence reflects volume-overloaded state
Clinical note: An S3 is usually caused by volume overload in congestive heart failure. It can also be associated with valvular disease, such as advanced mitral regurgitation, in which the “regurgitated” blood increases the rate of ventricular filling during early diastole.
4. S4: atrial gallop, S4: atrial contraction against a stiff ventricle, often heard after an acute myocardial infarction.
Clinical note: An S4 usually indicates decreased ventricular compliance (i.e., the ventricle does not relax as easily), which is commonly associated with ventricular hypertrophy or myocardial ischemia. An S4 is almost always present after an acute myocardial infarction. It is loudest at the apex with the patient in the left lateral decubitus position (lying on their left side).
Basic Properties of Gases
A. Dalton's Law of Partial Pressures
1. partial pressure - the "part" of the total air pressure caused by one component of a gas
Gas Percent Partial Pressure (P)
ALL AIR 100.0% 760 mm Hg
Nitrogen 78.6% 597 mm Hg (0.79 X 760)
Oxygen 20.9% l59 mm Hg (0.21 X 760)
CO2 0.04% 0.3 mm Hg (0.0004 X 760)
2. altitude - air pressure @ 10,000 ft = 563 mm Hg
3. scuba diving - air pressure @ 100 ft = 3000 mm Hg
B. Henry's Law of Gas Diffusion into Liquid
1. Henry's Law - a certain gas will diffuse INTO or OUT OF a liquid down its concentration gradient in proportion to its partial pressure
2. solubility - the ease with which a certain gas will "dissolve" into a liquid (like blood plasma)
HIGHest solubility in plasma Carbon Dioxide
Oxygen
LOWest solubility in plasma Nitrogen
C. Hyperbaric (Above normal pressure) Conditions
1. Creates HIGH gradient for gas entry into the body
2. therapeutic - oxygen forced into blood during: carbon monoxide poisoning, circulatory shock, asphyxiation, gangrene, tetanus, etc.
3. harmful - SCUBA divers may suffer the "bends" when they rise too quickly and Nitrogen gas "comes out of solution" and forms bubbles in the blood
The pituitary gland is pea-sized structure located at the base of the brain. In humans, it consists of two lobes:
- the Anterior Lobe and
- the Posterior Lobe
The Anterior Lobe
The anterior lobe contains six types of secretory cells All of them secrete their hormone in response to hormones reaching them from the hypothalamus of the brain.
Thyroid Stimulating Hormone (TSH)
TSH (also known as thyrotropin) is a glycoprotein The secretion of TSH is
- stimulated by the arrival of thyrotropin releasing hormone (TRH) from the hypothalamus.
- inhibited by the arrival of somatostatin from the hypothalamus.
TSH stimulates the thyroid gland to secrete its hormone thyroxine (T4).
Some develop antibodies against their own TSH receptors making more T4 causing hyperthyroidism. The condition is called thyrotoxicosis or Graves' disease.
Hormone deficiencies
A deficiency of TSH causes hypothyroidism: inadequate levels of T4 (and thus of T3 )..
Follicle-Stimulating Hormone (FSH)
FSH is a heterodimeric glycoprotein Synthesis and release of FSH is triggered by the arrival from the hypothalamus of gonadotropin-releasing hormone (GnRH).
FSH in females :In sexually-mature females, FSH (assisted by LH) acts on the follicle to stimulate it to release estrogens.
FSH in males :In mature males, FSH acts on spermatogonia stimulating (with the aid of testosterone) the production of sperm.
Luteinizing Hormone (LH)
LH is synthesized within the same pituitary cells as FSH and under the same stimulus (GnRH). It is also a heterodimeric glycoprotein
LH in females
In sexually-mature females, LH
- stimulates the follicle to secrete estrogen in the first half of the menstrual cycle
- a surge of LH triggers the completion of meiosis I of the egg and its release (ovulation) in the middle of the cycle
- stimulates the now-empty follicle to develop into the corpus luteum, which secretes progesterone during the latter half of the menstrual cycle.
LH in males
LH acts on the interstitial cells (also known as Leydig cells) of the testes stimulating them to synthesize and secrete the male sex hormone, testosterone.
LH in males is also known as interstitial cell stimulating hormone (ICSH).
Prolactin (PRL)
Prolactin is a protein of 198 amino acids. During pregnancy it helps in the preparation of the breasts for future milk production. After birth, prolactin promotes the synthesis of milk.
Prolactin secretion is
- stimulated by TRH
- repressed by estrogens and dopamine.
Growth Hormone (GH)
- Human growth hormone (also called somatotropin) is a protein
- The GH-secreting cells are stimulated to synthesize and release GH by the intermittent arrival of growth hormone releasing hormone (GHRH) from the hypothalamus. GH promotes body growth
In Child
- hyposecretion of GH produces dwarfism
- hypersecretion leads to gigantism
In adults, a hypersecretion of GH leads to acromegaly.
ACTH — the adrenocorticotropic hormone
ACTH acts on the cells of the adrenal cortex, stimulating them to produce
- glucocorticoids, like cortisol
- mineralocorticoids, like aldosterone
- androgens (male sex hormones, like testosterone
Hypersecretion of ACTH cause of Cushing's disease.