Chapter 10 - Homeostasis Flashcards
What are the main functions if the excretory system?
4
Regulate…
- Blood pressure
- Blood osmolarity
- Acid-base balance
- Removal of nitrogenous wastes
What do AFFERENT and EFFERENT arterioles do?
Afferent arteriole: goes from the artery through the medulla and to the cortex
Efferent arteriole: lead blood away from AFFERENT arterioles to the second capillary bed.
What structures does the blood pass through in the kidneys / to get through the nephron?
Renal artery Afferent arteriole Glomerulus / Bowman's capsule (First capillary bed) Efferent arteriole (Second capillary bed) - "vasa recta" Proximal convoluted tubule Loop of henle Distal convoluted tubule Collecting duct
What is the vasa recta?
The capillaries that surround the loop of henle (second capillary bed)
What is the DETRUSOR muscle?
Muscle associated with the internal urethral sphincter
Stretch receptors detect bladder is full
Parasympathetic neurons fire
Detrusor muscle CONTRACTS
Internal sphincter relaxes
Micturition reflex
The contraction of the DETRUSOR muscle leads to the relaxation of the internal urethral sphincter
How does one urinate?
Voluntary control of external urethral sphincter
Urination is facilitated by the contraction of abdominal musculature, which creates pressure in the abdominal cavity and hence pressure on the bladder –> increases urinary flow rate
What is the MAIN role of the kidneys?
To regulate blood volume and osmolarity
What are the the main functions of the kidneys:
- Filtration
- Secretion
- Reabsorption
What is a portal system?
Consists of two capillary beds through which blood must travel before returning to the heart
What are the three main portal systems in the body?
- Kidney portal system
- Hypophyseal postal system (connects hypothalamus and ant pituitary)
- Hepatic portal system (connects the gut tube and the liver)
WHAT IS (brief) filtration, secretion, and re absorption:
FILTRATION: movement of SOLUTES from the blood to the filtrate at Bowman’s capsule
SECRETION: movement of SOLUTES from blood to filtrate anywhere but the capsule
REABSORPTION: movement of SOLUTES from filtrate BACK TO BLOOD
How is the glomerulus like a sieve?
Small molecules dissolved in the blood will pass through the tiny pores
(Glucose)
Large molecules will not, and be removed into the urine
(Blood cells, proteins)
**Blood cells or proteins found in the urine indicate a problem with the glomerulus
What are Starling forces?
Results in the movement of fluid into Bowman’s space
Account for the pressure differential between the blood and Bowman’s space
(Account for both HYDROSTATIC and ONCOTIC pressure differences)
Hydrostatic pressure versus osmolarity in the glomerulus / Bowman’s space
Hydrostatic pressure: higher pressure in the glomerulus so fluid wants to move to Bowman’s space
Osmotic pressure: higher concentration of solutes in the glomerulus so fluid would want to move TO the glomerulus
BUT HYDROSTATIC PRESSURE IS MUCH GREATER
Usually, fluid flows from glomerulus to Bowman’s space. What might cause de-arrangement of this?
Obstructed ureter (ie kidney stone)
How much (volume) of blood is filtered by the kidneys?
180 liters per day is filtered
This is about 36 times the amount of blood we have (4.7-5 L)
Aka, our entire volume of blood is filtered approx every 40 mins
What substances are typically reabsorbed from the filtrate?
Glucose
Amino acids
Vitamins
ALSO A LOT OF WATER, ie ADH and aldosterone can alter quantity of water re absorbed at the kidney to maintain blood pressure
What substances are typically “waste” and not re absorbed?
Hydrogen ions
Potassium ions
Ammonia / urea
“HUNK”
H+
Urea
NH2
K+
What happens at the PROXIMAL CONVOLUTED TUBULE?
(Closest to the capsule)
REABSORPTION Of the things the body wants to keep -glucose -amino acids -water soluble vitamins -salts -WATER
SECRETION From the blood into the filtrate -hydrogen -potassium -ammonia and urea
What is the interstitium?
What happens to solutes that end up here?
The connective tissue that surrounds the nephron
Solutes here are picked up by the vasa recta and hence returned to the blood
What happens at the DESCENDING LOOP OF HENLE?
Only permeable to water
Goes deep into the medulla, which has INCREASING osmolarity
Water flows out from the filtrate to the medulla (aka the interstitium) and goes to the vasa recta to go back into the blood
How can the kidneys change osmolarity in the medulla?
Why?
The medulla can be isotonic with blood (when the body wants to excrete water)
The medulla can be up to four times as concentrated (when it wants to conserve water and maximize reabsorption)
In order to get maximum reabsorption and conserve water
What is the COUNTER-CURRENT MULTIPLIER SYSTEM?
The flow of filtrate through the loop of henle is in the opposite direction as the flow of blood in the vasa recta.
This is to prevent equilibrium (if they both were going in the same direction) and allows max reabsorption of water!
What happens at the ASCENDING LOOP OF HENLE?
Only permeable to SALTS
Due to high concentrations of salt at the medulla and decrease as the loop goes up, salt moves out from the filtrate as it goes up.
Comment on the thickness of the loop of henle
Thickens as the ASCENDING loop moves to the outer medulla.
The loop itself not thicker but cells around it are larger and contain a lot f MITOCHONDRIA to actively transport sodium and chloride.
What is the diluting segment of the loop?
The thick portion
So much Na and Cl is re absorbed that the filtrate (urine) is more dilated than the blood!
This is the only place that this may happen
This is useful when over hydrated and needing to get rid of water
Filtrate at the beginning at the loop is isotonic to the interstitium. How does it compare at the end?
It is a bit more diluted (lower osmolarity than the interstitium)
What happens at the DISTAL CONVOLUTED TUBULE?
ALDOSTERONE can act on the DCT
Promotes reabsorption of sodium, and water tends to follow
Also, more waste secretion (like the PCT)
What happens at the COLLECTING DUCT?
Final concentration of urine.
Both ADH and aldosterone act here.
More permeable duct: more water and salt can be re absorbed, creating a very concentrated urine
*ADH and aldosterone encourage this
Less permeable duct: nothing passes easily, water and sodium stays in the collecting duct and is excrete in urine. This happens when the body is well hydrated.
How do DIURETIC drugs affect the nephron?
Diuretic drugs increase the amount of water in the urine
For example when there is edema in the lungs or tissues resulting from congestive heart failure
Diuretic decrease the ability of sodium to be reabsorbed, giving the filtrate higher osmolarity which pulls water INTO the filtrate (hence discourages excess fluid in the tissues / edema)
At the end of the collecting duct, why does the filtrate contain? (Ie what are the waste products in urine?)
Urea
Uric acid
Excess ions Sodium Potassium Magnesium Calcium
ALDOSTERONE versus ADH:
Aldosterone:
- steroid hormone
- Secreted in response to DECREASED blood pressure
- Affects both salt and water reabsorption hence no effect on osmolarity
ADH:
- peptide hormone
- Secreted in response to INCREASED BLOOD OSMOLARITY
- only affects water reabsorption (a uses a change in osmolarity!)
ALDOSTERONE
Where is it secreted?
How is it activated?
How does it affect the kidneys and blood volume?
Secreted by the adrenal cortex
Responds to deceased blood pressure
ACTIVATION: Decreased BP Renin secreted (juntaglomerular cells) Angiotensinogen (+ renin) -> Angiot. I Angiot. I (+ ACE) --> Angiotensin II Angiotensin II promotes ALDOSTERONE RELEASE
Aldosterone increases DCT and collecting duct reabsorption of sodium
Water follows, creating higher blood volume and hence higher blood pressure
ADH / vasopressin
Where is it secreted?
How is it activated?
How does it affect the kidneys and blood volume?
Made in the hypothalamus, secreted by post pit
Secreted in response to high blood osmolarity
Alters permeability of the collecting duct - makes the cell junctions “leaky” so more water can be reabsorbed, hence decreasing blood osmolarity
Alcohol and caffeine inhibit ADH (lead to diluted urine and frequent urination)
How does vasoconstriction / vasodilation affect renin production?
Constriction of the AFFERENT arteriole leads to less blood entering the glomerulus
This indicated a lower blood pressure to the juxtaglomerular cells, and they release renin and eventually activate aldosterone (which will raise blood pressure)
Blood osmotic pressure versus ONCOTIC pressure:
Osmotic: the concentration of solutes
ONCOTIC: the “pull” created by large plasma protein (or albumin) that can’t leave the vessel.
Ie: if plasma proteins are lost in the urine (malnutrition), oncotic pressure is reduced and fluid will be reabsorbed even more than usual - this can lead to edema
What is a normal level of blood osmotic pressure?
290 milliosmoles(mOsm)
What do the nephrons secrete into the tubules?
How is this done?
Salts
Acids
Bases
Urea
By either active or passive transport
Secretion is also a way to excrete wastes that are too large to pass through the glomerulus
What role does the excretory system play in acid-base balance?
CAN SELECTIVELY INCREASE OR DECREASE SECRETION OF H+ and HCO3-
If pH is low: (acidic)
Kidneys excrete hydrogen, and reabsorbed more bicarbonate (making the blood less acidic)
If pH is too high: (basic)
The bicarbonate will be excreted while H+ ions are reabsorbed (to make the blood less basic)
**this is slower than the respiratory response, but highly effective
Four roles of skin:
- Physical barrier
- UV protection
- Transduction of sensory info
- Thermoregulation
What does keratin do?
Protects against injury, water, and pathogens
Resistant to damage
Main cells of skin
Also forms hair and fingernails
Layers of the epidermis (5)
Come Let’s Get Sun Burned
Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale
Brief description if each layer of the epidermis:
Corneum - flattened layers of keratinocytes (barrier)
Lucidum - only in thick, hairless skin such as soles of hands and feet (transparent)
Granulosum - where keratinocytes die and lose their nucleus
Spinosum - Langerhan cells
Basale - stem cells, proliferation of keratinocytes
Where are melanocytes found?
What are they derived from?
Relation to skin tone
They are found in the stratum basale
Formed from NEURAL CREST CELLS
Make melanin
More melanocytes activity –> darker skin tone
(More UV radiation –> more active melanocytes –> tan!)
What does melanin do?
Protects the skin from DNA damage due to UV radiation
Once produced, melanin pigment is passed to the keratinocytes
What is albinism?
What is vitiligo?
Albinism: inability to synthesize melanin
Vitiligo: melanocytes are killed (autoimmune disorder)
What are Langerhan cells?
Special macrophages that reside in tissue in the stratum spinosum
Can present antigens to T-cells in order to activate immune response
What are the two layers of the DERMIS?
What thins are found in the dermis in general? (3)
Papillary layer (just below the epidermis) - loose CT
Reticular layer (just above the hypodermis) - more dense
Sweat glands, hair follicles, blood vessels
What are some sensory cells and nerve endings found in the dermis:
(4)
MERKEL CELLS
Located at epidermal / dermal junction
Deep pressure and texture sensations
FREE NERVE ENDINGS
Respond to pain
*Meissner’s corpuscles
Respond to light touch
*Ruffini endings
Respond to stretch
*Pacinian corpuscles
Respond to deep pressure & vibration
What is “sweating”?
What are sweat glands innervated by?
Autonomic nervous system - cooling mechanism. Dictated by body temp rising above a set temperature determined by the hypothalamus
Postganglionic sympathetic neurons that use acetylcholine innervated the sweat glands
What is the mechanism of sweating and how does it reduce temperature?
Neurons innervated sweat glands Secrete water + ions Water + energy = evaporation (Requires energy from the body) ENDOTHERMIC process
At the same time, arteriolar vasodilation occurs to maximize heat loss (bring lots of blood to the skin and maximize amount of heat available to evaporate sweat)
Why are there solutes in sweat?
They increase he boiling point slightly, hence requiring more energy to evaporate!
What is piloerection and how does it help heat the body?
What happens with arterioles?
Arrector pollo muscles contract and raise hairs on the body, trapping a layer of heated air near the skin
Simultaneously, arterioles constrict, limiting blood around the skin.
What is shivering?
How does shivering contribute to increasing body temperature?
Rapid contraction of skeletal muscle.
Requires a lot of ATP, but a good position of energy from the ATP is lost as heat.
White and brown fat
White fat: layer of fat under the skin for insulation
Brown fat: may he present especially in infants. Much less efficient electron transport chain, which means more heat energy is released as ATP is used.
How does the skin contribute to osmolarity?
It is relatively impermeable to water.
Prevents both water intake and water loss.
Important in cases of burns, large losses of skin (these result in dehydration of the skin)
What is found in the hypodermis?
Fat and connective tissue
Connects skin to the rest of the body
What is the neuromuscular junction, and what happens here?
What is the nerve terminal + the myocytes called?
Where the nervous and muscular systems meet - at the motor neuron’s synapse where it activates the muscle
Acetylcholine binds to receptors ON THE SARCOLEMMA, causing depolarization
Each nerve terminal controls a group of myocytes, aka a muscle!
(Many myofibrils wrapped in sarcolemma make up a MYOCYTE aka muscle cell!)
Called a MOTOR UNIT
What actions does the action potential trigger in a muscle cell?
- Depolarization
- Action potential spread to T-tubule
- T-tubule travels to the sarcoplasmic reticulum
- Action potential researches SR and releases calcium
- Calcium binds to TROPONIN
- Troponin is bound to tropomyosin, so the calcium creates a change in the conformation of TROPOMYOSIN
- This exposes MYOSIN-BINDING sites on the actin filament.
- Myosin binds to this site, pulling the actin filament
- Sarcomere shortens
What is hydrolyzed ATP and where is it found?
Why is it important / what is it’s role?
ADP plus an inorganic phosphate (Pi)
Carried by myosin
Release of ADP+Pi from myosin provides the energy for the POWERSTROKE and results in sliding of the actin filament over the myosin filament
ATP then binds to myosin head, releasing it from actin.
What happens to myosin when ATP is hydrolyzed into ADP+Pi ?
RECOCKS the myosin head so that it is ready to initiate another cross-bridge cycle.
“Sliding filament model”
What does acetylcholinesterase do at the synapse?
It degrades acetylcholine
This terminates the signal and allows sarcolemma to repolarize
