1. Steps of gas transfer in muscles:
- From the lungs, oxygen is carried by the hemoglobin molecule.
One hemeglobin molecule can bind to four oxygen molecules. Oxygen
and carbon dioxide gases can easily diffuse across the plasma
membrane of tissues.
- Muscles are highly vascular tissues and muscle fibers are
heavily intertwined with tiny capillaries, which supply oxygen to
muscle fibers and remove waste products such as carbon dioxide and
lactic acid.
- As oxygenated blood reached muscle cells, oxygen diffuses
across the sarcolemma, plasma membrane of muscle cells.
- The process of gas transfer happens because of Bohr effect-
carbon dioxide diffuses into blood stream and red blood cell turns
it into bicarbonate ion, and an increase in carbon dioxide levels
lowers the pH of blood causing hemoglobin to release oxygen.
- Once oxygen is diffused into the cell, it has two fates: 1.
Bind to myoglobin- a protein that acts like hemoglobin and binds
oxygen. Muscles use this protein to store small amounts of oxygen
for a later use, OR 2. It can be used in the electron transport
chain in mitochondrion to accept H+ ions produced by the oxidation
of carbohydrates and fats. It can combine with H+ ions to form
water. This process of oxidation produces water, ATP, heat, and
carbon dioxide, and it is called internal respiration.
2. Steps of Urine formation in kidneys:
- Functional unit of kidney is nephrons which contain specialized
capillaries called glomerulus. Glomerulus is
formed by afferent arteriole and is lined by a space called
bowman's capsule where urine is filtered
into.
- The filtration barrier is made up of 3 main components: a.
Endothelial cells of glomerular capillaries, b.
Glomerular basement membrane, c.
Epithelial cells of bowman's capsule called
Podocytes.
- Endothelial cells contain small fenestrations that limit the
filtration of cells like RBCs but permit filtration of proteins,
large molecules and water. They also contain glycocalyx which
hinders diffusion of anions. Podocytes also restrict the filtration
of anions.
- Basement membrane contains type IV collagen, heparan sulfate,
proteoglycans which limit anion diffusion and large solute
filtration.
- From the capsule, urine enters proximal convoluted tubule
(PCT) which reaborbs all glucose and amino acids,
bicarbonate, sodium, chloride, phosphate, potassium, water, and
uric acid. PCT also generates NH3 and secretes more hydrogen
ions.
- From PCT, urine enters thin descending loop of
Henle, which reabsorbs water into interstitium lined with
vasa recta (tiny capillaries). This segment is impermeable to Na+
which makes the urine hypertonic. Parathyroid
hormone increases phosphate excretion and angiotensin II increases
Na+, H2O, and bicarbonate reabsorption.
- From thin ascending loop, urine enters thick ascending
loop of Henle, which reabsorbs Na+, K+ and Cl-, also
induces paracellular reabsorption of Mg+ and Ca2+ though positive
lumen potential generated by k+ reabsorption. This segment is
impermeable to water so makes the urine less concentrated.
- From thin ascending loop, urine enters distal convoluted tubule
(DCT), which reabsorbs Na+, Cl-. This segment is also impermeable
to water which makes urine more dilute (hypotonic). Parathyroid
hormone increases Ca2+/Na+ exchange to increase Ca2+
reabsoption.
- Finally urine enters collecting duct where Na+ reabsorbs in
exchange for K+ and H+ regulated by aldosterone. Antidiuretic
hormone (ADH) acts to insert aquaporin channels on principal cells
of collecting ducts to reabsorp water in certain situations like
dehydration.
- From collecting duct, urine enters papillary duct----> minor
calyx----> major calyx----> renal pelvis---->
ureter----> urinary bladder.
3. Correlation between Urinary, Respiratory, Circulatory system:
a. Oxygen and nutrient delivery, b. Acid- base balance, c. Waste
removal, d.Blood Volume and Blood Pressure regulation.
- A. Circulatory system delivers oxygen and essential nutrients
to the urinary and respiratory system. It also transports CO2 from
the tissues in the form of bicarbonate.
- B. Acid-base balance: respiratory and urinary systems play a
crucial role in regulating pH chnages. They act buffer systems when
there is a change in blood pH. During metabolic acidosis or
alkalosis when kidneys strive to normalize pH, respiratory system
acts as the compensatory system rapidly removing carbon dioxide to
increase or decrease blood pH. During respiratory acidosis or
alkalosis, urinary system acts as compensatory system quickly
excreting bicarbonate to increase or decrease blood pH.
- C. Waste removal: respiratory and urinary also function to
remove waste products such as CO2 (through inhalation), and
ammonia, urea, creatinine, excess electrolytes like potassium
through urinary excretion.
- D. Blood Volume and Blood Pressure regulation: urinary system
maintains blood pressure in the circulatory system which in turn
maintains steady organ perfusion. Kidneys produce renin which
increases Na+ and H2O reabsorption to increase blood volume. It
increases the sympathetic effects across the body to maintain
pressure.