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.
How does change in concentration effects the concentration of urine?
If there is a higher solute concentration in the interstitum water moves out of the loop and is absorbed and urine becomes more concentrated.
If there is less solute concentration in interstitum water moves into the loop and is secreted and urine is more diluted.
Countercurrent multiplier system
Serves to maximize reabsorption into the interstitum.
Occurs because the filtrate in the tubule and the blood in the interstitum (the vasa racta surrounding the loop of Henle) flow in opposite directions. This causes blood in interstitum to become hypertonic which maximizes reabsorption from the tubule.
What is the largest organ of our body?
The skin ( integument) which is a big component of the nonspecific immune system.
Describe the layers of the skin
From furthest down lower to the topmost layer.
Hypodermis
Dermis
Epidermis- The epidermis is divided into sublayers called strata:
- Stratum basalae
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Stratum corneum
Describe the components of the stratum basale
Contains stem cells
Contains keratinocytes which produces keratin and melanocytes which produces melanin ( serves to protect us from UV damage to DNA, skin tone dictated by how active theses cells are).
Describe the function of the stratum spinosum
Contains largerhan cells ( macrophages that exposes antigens to T- cells for immune system activation) and is the site where keratinocytes connect to each other.
Keratinocytes
Main cell of the epidermis.
Produces keratin which serves to protect the skin and resist skin to damage.
Hair and fingernails are also made from keratin.
Describe the function of the stratum granulosum
Where keratinocytes die and lose their nuclei.
Describe the function of stratum lucidum
Only located in thick, hairless skin
Describe the function of the stratum corneum
Contains layers flattened keratinocytes which protects against pathogen invasion.
Contains hair cells with openings for sweat glands and sebacous glands ( which secretes sebum which serves to lubricate the skin and prevent skin from drying out).
Calluses
Areas of excessive keratin which is caused by repeated friction.
The body’s attempt to resist further damage.
Describe the layers of the dermis
The papillary layer which is below the epidermis and contains loos connective tissue.
Below the papillary layer is the reticular layer.
Sweat glands, blood vessels, and hair cells originate from here.
Describe the sensory receptors in the skin ( mechanoreceptors)
- Market cells
- Meissner corpuscles
- Ruffini endings
- Pacinian corpuscles
They reside in the dermis.
- Market cells - respond to deep pressure and texture.
- Meissner corpuscles - responds to light touch.
- Ruffini endings- responds to stretch.
- Pacinian corpuscles- responds to deep pressure and vibrations.
Describes the hypodermis layer of the skin
connects the skin to the rest of the body and contains fat and fibrous tissue.
How does the skin participate in thermoregulation in hot conditions
Once the internal body temperature crosses over a certain point it’s detected by the hypothalamus.
This starts the postganglionic neurons secrete Ach onto the sweat glands which releases salt and water. The evaporation of this cools us down.
Vasodilation allows the movement of more blood and therefore dissipation of more heat.
How does the skin participate in thermoregulation in cold environments
In cold conditions pilli muscles contract causing hair cells to become erect and heat to be trapped below.
Shivering caused by repeated contractions of skeletal muscle generates heat but this requires a lot of ATP.
Adults contains white fat which helps insulate us. Babies contains brown fat which uses more energy and so produces more heat.
