MCAT Homeostasis Flashcards
What roles does the excretory system carry out?
Play a role in eliminating wastes, acid- base balance, blood osmolarity, blood pressure, removal of nitrogenous wastes.
A big player in the excretory system is the kidneys.
Describe the anatomy of the kidneys
The nephron is the functional unit of the kidneys. They empty into the renal pelvis which is the wide part of the kidney. The renal pelvis turns into the ureter.
The cortex is the outermost part of the kidneys while the medulla is the innermost part and is located in the cortex.
The renal helium is the groove on the inside curvature of the kidneys. It’s where the renal arteries and renal veins enter and exit. The widest part of the renal helium is the renal pelvis.
Describe the renal portal system
Renal artery enters the renal pelvis, and their afferent arterioles branches out at the nephrons forming the primary bed.
From the nephrons efferent arterioles terminate at the glomerulus forming the secondary capillary bed.
Vasa recta
The term given to the capillaries that surrounds the loop of Henle.
Which part of the nervous system controls our bladder?
Parasympathetic NS
Describe the process of urination
When we have to urinate, the parasympathetic nervous system causes our detrusor muscle to contract.
Detrusor muscle contraction causes relaxation of the internal urethral sphincter (controlled by autonomic NS, smooth muscle). From here we can decide to relax our external urethral sphincter or keep it contracted (somatic, skeletal muscle).
What is the primary job of the kidneys?
What processes does the kidneys carry out to carry out their job?
Regulate blood volume and blood osmolarity
- Filtration
- Secretion
3.Reabsorption
Describe the process of filtration in the kidneys
Blood passes from the glomerulus where it’s filtered and becomes the filtrate and enters the bowman’s space.
The movement of blood from the glomerulus to bowman’s space is governed by starling forces.
Anything that is too large doesn’t get filtered and is moved to the vasa racta by efferent arterioles.
Starling forces
The pressure differentials between the blood and bowman’s capsule caused by differences in the oncotic and hydrostatic pressures.
Describe the process of secretion in the kidneys
The kidneys get rid of what the body doesn’t need and keeps what the body needs.
Directly related to what our body needs at the time.
Describe the process of reabsorption by the kidneys
The kidneys can uptake compounds that were filtered if the body needs them.
What are the two primary goals of the kidneys?
Keep what the body needs and get rid of what it doesn’t
Conserve water by making urine more concentrated
Horizontal elements of the kidneys v. Vertical elements
Horizontal elements are concerned with keeping what the body needs and getting rid of what it doesn’t.
Vertical elements are concerned with concentrating urine and the volume.
Proximal convoluted tubule
A horizontal element of the nephron.
Absorbs amino acids, glucose, salts, and water- soluble vitamins.
The filtrate remains isotonic with the interstitum and any compounds that move into interstitum will be picked up by the vasa racta and dumped back into circulation.
PCT dumps “ HUNK”
H+
Urea
NH3
K+
Loop of Henle (vertical element)
Filtrate moves from the proximal convoluted tubule to loop of Henle.
The descending loop extends deep into the medulla before turning around and forming the ascending loop of Henle which enters the outer medulla.
The descending loop is only permeable to water. The kidneys can alter the osmolarity of the interstitum to maximize reabsorption and concentration of urine.
Under physiological conditions the osmolarity interstitum and loop of Henle are the same.
