NEET MDS Lessons
Physiology
Production of Hormones
The kidneys produce and interact with several hormones that are involved in the control of systems outside of the urinary system.
Calcitriol. Calcitriol is the active form of vitamin D in the human body. It is produced by the kidneys from precursor molecules produced by UV radiation striking the skin. Calcitriol works together with parathyroid hormone (PTH) to raise the level of calcium ions in the bloodstream. When the level of calcium ions in the blood drops below a threshold level, the parathyroid glands release PTH, which in turn stimulates the kidneys to release calcitriol. Calcitriol promotes the small intestine to absorb calcium from food and deposit it into the bloodstream. It also stimulates the osteoclasts of the skeletal system to break down bone matrix to release calcium ions into the blood.
Erythropoietin. Erythropoietin, also known as EPO, is a hormone that is produced by the kidneys to stimulate the production of red blood cells. The kidneys monitor the condition of the blood that passes through their capillaries, including the oxygen-carrying capacity of the blood. When the blood becomes hypoxic, meaning that it is carrying deficient levels of oxygen, cells lining the capillaries begin producing EPO and release it into the bloodstream. EPO travels through the blood to the red bone marrow, where it stimulates hematopoietic cells to increase their rate of red blood cell production. Red blood cells contain hemoglobin, which greatly increases the blood’s oxygen-carrying capacity and effectively ends the hypoxic conditions.
Renin. Renin is not a hormone itself, but an enzyme that the kidneys produce to start the renin-angiotensin system (RAS). The RAS increases blood volume and blood pressure in response to low blood pressure, blood loss, or dehydration. Renin is released into the blood where it catalyzes angiotensinogen from the liver into angiotensin I. Angiotensin I is further catalyzed by another enzyme into Angiotensin II.
Angiotensin II stimulates several processes, including stimulating the adrenal cortex to produce the hormone aldosterone. Aldosterone then changes the function of the kidneys to increase the reabsorption of water and sodium ions into the blood, increasing blood volume and raising blood pressure. Negative feedback from increased blood pressure finally turns off the RAS to maintain healthy blood pressure levels.
Chemical Controls of Respiration
A. Chemoreceptors (CO2, O2, H+)
1. central chemoreceptors - located in the medulla
2. peripheral chemoreceptors - large vessels of neck
B. Carbon Dioxide Effects
1. a powerful chemical regulator of breathing by increasing H+ (lowering pH)
a. hypercapnia Carbon Dioxide increases ->
Carbonic Acid increases ->
pH of CSF decreases (higher H+)- >
DEPTH & RATE increase (hyperventilation)
b. hypocapnia - abnormally low Carbon Dioxide levels which can be produced by excessive hyperventilation; breathing into paper bag increases blood Carbon Dioxide levels
C. Oxygen Effects
1. aortic and carotid bodies - oxygen chemoreceptors
2. slight Ox decrease - modulate Carb Diox receptors
3. large Ox decrease - stimulate increase ventilation
4. hypoxic drive - chronic elevation of Carb Diox (due to disease) causes Oxygen levels to have greater effect on regulation of breathing
D. pH Effects (H+ ion)
1. acidosis - acid buildup (H+) in blood, leads to increased RATE and DEPTH (lactic acid)
E. Overview of Chemical Effects
Chemical Breathing Effect
increased Carbon Dioxide (more H+) increase
decreased Carbon Dioxide (less H+) decrease
slight decrease in Oxygen effect CO2 system
large decrease in Oxygen increase ventilation
decreased pH (more H+) increase
increased pH (less H+) decrease
Biological Functions are Extremely Sensitive to pH
- H+ and OH- ions get special attention because they are very reactive
- Substance which donates H+ ions to solution = acid
- Substance which donates OH- ions to solution = base
- Because we deal with H ions over a very wide range of concentration, physiologists have devised a logarithmic unit, pH, to deal with it
- pH = - log [H+]
- [H+] is the H ion concentration in moles/liter
- Because of the way it is defined a high pH indicates low H ion and a low pH indicates high H ion- it takes a while to get used to the strange definition
- Also because of the way it is defined, a change of 1 pH unit means a 10X change in the concentration of H ions
- If pH changes by 2 units the H+ concentration changes by 10 X 10 = 100 times
- Human blood pH is 7.4
- Blood pH above 7.4 = alkalosis
- Blood pH below 7.4 = acidosis
- Body must get rid of ~15 moles of potential acid/day (mostly CO2)
- CO2 reacts with water to form carbonic acid (H2CO3)
- Done mostly by lungs & kidney
- In neutralization H+ and OH- react to form water
- If the pH changes charges on molecules also change, especially charges on proteins
- This changes the reactivity of proteins such as enzymes
- Large pH changes occur as food passes through the intestines.
Functions of the nervous system:
1) Integration of body processes
2) Control of voluntary effectors (skeletal muscles), and mediation of voluntary reflexes.
3) Control of involuntary effectors ( smooth muscle, cardiac muscle, glands) and mediation of autonomic reflexes (heart rate, blood pressure, glandular secretion, etc.)
4) Response to stimuli
5) Responsible for conscious thought and perception, emotions, personality, the mind.
Bronchitis = Irreversible Bronchioconstriction
. Causes - Infection, Air polution, cigarette smoke
a. Primary Defect = Enlargement & Over Activity of Mucous Glands, Secretions very viscous
b. Hypertrophy & hyperplasia, Narrows & Blocks bronchi, Lumen of airway, significantly narrow
c. Impaired Clearance by mucocillary elevator
d. Microorganism retension in lower airways,Prone to Infectious Bronchitis, Pneumonia
e. Permanent Inflamatory Changes IN epithelium, Narrows walls, Symptoms, Excessive sputum, coughing
f. CAN CAUSE EMPHYSEMA
(RDS) Respiratory distress of Newborn
1. hyaline membrane disease of the new born
2. decrease in surfactant, Weak, Abnormal complience of chest wall
3. Small alveoli, difficult to inflate, Alveoli tent to collapse, many of varied sizes
4. decrease in O2 diffusion area, lung difficult to expand, in compliance
Maintenance of Homeostasis
The kidneys maintain the homeostasis of several important internal conditions by controlling the excretion of substances out of the body.
Ions. The kidney can control the excretion of potassium, sodium, calcium, magnesium, phosphate, and chloride ions into urine. In cases where these ions reach a higher than normal concentration, the kidneys can increase their excretion out of the body to return them to a normal level. Conversely, the kidneys can conserve these ions when they are present in lower than normal levels by allowing the ions to be reabsorbed into the blood during filtration. (See more about ions.)
pH. The kidneys monitor and regulate the levels of hydrogen ions (H+) and bicarbonate ions in the blood to control blood pH. H+ ions are produced as a natural byproduct of the metabolism of dietary proteins and accumulate in the blood over time. The kidneys excrete excess H+ ions into urine for elimination from the body. The kidneys also conserve bicarbonate ions, which act as important pH buffers in the blood.
Osmolarity. The cells of the body need to grow in an isotonic environment in order to maintain their fluid and electrolyte balance. The kidneys maintain the body’s osmotic balance by controlling the amount of water that is filtered out of the blood and excreted into urine. When a person consumes a large amount of water, the kidneys reduce their reabsorption of water to allow the excess water to be excreted in urine. This results in the production of dilute, watery urine. In the case of the body being dehydrated, the kidneys reabsorb as much water as possible back into the blood to produce highly concentrated urine full of excreted ions and wastes. The changes in excretion of water are controlled by antidiuretic hormone (ADH). ADH is produced in the hypothalamus and released by the posterior pituitary gland to help the body retain water.
Blood Pressure. The kidneys monitor the body’s blood pressure to help maintain homeostasis. When blood pressure is elevated, the kidneys can help to reduce blood pressure by reducing the volume of blood in the body. The kidneys are able to reduce blood volume by reducing the reabsorption of water into the blood and producing watery, dilute urine. When blood pressure becomes too low, the kidneys can produce the enzyme renin to constrict blood vessels and produce concentrated urine, which allows more water to remain in the blood.