Homeostasis Flashcards
In broad terms and in relation to homesotatic mechanisms, the body “effectors” are
Muscles and Glands
What are homeostatic responses generally aimed at maintaining ?
The internal Milieu, i.e. physico-chemical conditions in the ECF
Homeostatic mechanisms generally respond to …
A. changing variables, which therefore tend to oscillate
B. Deviations from the set point
What is negative feedback ?
When the effector negates the stimulus.
What is the difference between positive and negative feedback?
Positive feedback occurs to INCREASE the change or output: the result of a reaction is amplified to make it occur more quickly. Negative feedback occurs to REDUCE the change or output: the result of a reaction is reduced to bring the system back to a stable state.
What is a set point?
Is a balanced physiological value for a variable.
What is a sensor ?
Sensor or receptor monitors variations from the set point and detects the change.
What is integration?
The integration or control center takes the received information and sends signals to effectors.
What is an effector ?
any muscles or glands that receives information from the integrating center and acts to bring about the changes needed to maintain homeostasis.
What is oscillation?
The value always oscillates about the set point in a system controlled by negative feedback.
What is the difference between efficient and less efficient ?
The efficient has low tolerance for change and requires high levels of ATP.
A less efficient has high tolerance for change and it will take more time to response because oscillations will be larger.
What is a circadian rhythm ?
The set points of some controlled variables are not constantly and can vary, often with the diurnal (circadian) rhythm approximately a 24 hour daily cycle.
An example is the temperature (1 or 2 while slepping) and the cortisol secretion.
What are the components of human thermoregulatory homeostatic system when increasing the temperature?
1.Stimulus: blood temperature warmer than hypothalamic set point.
2. It activated the heat loss center in the hypothalamus: Skin blood vessels and integumentary system.
3. The body temperature decreases and the hypothalamus heat-loss center shuts-off
The body temeperature is usually ?
35.8c-38.2c
What happen with skin blood vessels and sweat glands work to decrease the body temperature?
*Skin blood vessels: they dilate capillaries become flushed with warm blood, heat radiates from skin surface.
*Sweat glands: secrete perspiration, which is vaporized by the body heat, helping to cool it down.
What are the components of human thermoregulatory homeostatic system when DECREASING the temperature?
1.Stimulus: blood temperature cooler than hypothalamic set point.
2. It activated the heat promoting center in the hypothalamus: Skin blood vessels and skeletal muscles
3. The body temperature increases and the hypothalamus heat promoting center shuts-off
What happen with skin blood vessels and skeletal muscle work to increase the body temperature?
The skin blood vessels: constrict blood is diversify from skin capillaries and withdrawn to deeper tissues; minimizes overall heat loss from skin surface.
What are the two types of receptor that participate in thermoregulation homeostasis?
*Shell or peripheral receptors
*Deep body temperature receptors
Describe how and why fever is generated, and what aspects of homeostatic control are altered during a feverish period
-During inflammation e.g. infection, autoimmune disorders, macrophages and other cells release cytokines- interleukins, tumour necrosis factor.
-Cytokines act on the hypothalamus - release prostaglandins which reseat the hypothalamic set point to a higher level- heat promoting mechanisms activated.
-Vasoconstriction, reduced heat loss, skin cools, shivering commences and chills as body temperature rises.
-Once the immune system (+antibiotics/antiviral drugs) has reversed the disease process, the hypothalamic set point returns to normal.
-Heat loss mechanism is activated
*Fever mau assist control of infections by increasing the metabolic rate, increasing phagocytic activity (neutrophils) and inhibition of bacteria growth (increased temperature, sequestration of iron, copper and zinc by the liver)
Describe one of the examples you were given of positive feedback.
Regulation of clotting
1. Break or tear in blood vessel wall
2. clotting occurs as platelets adhere to site and release chemicals.
3. release chemicals attract more platelets.
4.Clotting proceeds until brake is sealed by newly formed clot.
Give another example of positive feedback
1- push baby against the cervix
2. the cervical stretch
3. Stimulates the production in the hypothalamus of oxytocin
4. oxytocin is stored by the posterior pituitary and released in the bloodstream.
5. Oxytocin causes uterine contraction
the delivery of the baby stops the cycle
What is the difference between normal positive feedback
They are limited duration loops and they stop when the process had been driven to completion.
Where is the nephrone located?
In the kidneys
What does the nephron do ?
*It filters the blood fluid via nephrones
*Almost all of this fluid, and everything it contains is reabsorbed and returned to the body.
* Toxic wastes are excreted, and the amount of water and salt retained or lost in the final urine or will depend on the bodies needs.
Describe how Na+ and water are reabsorbed in the proximal convoluted tubule
-Na+ is removed from the cells lining the PCT by the Na+/K+ ATPase pump. the resultant concentration gradient between the lumen of the nephron and the inside of the cells allows for the facilitated transport of NA+ intro cells lining the PCT. water follows sodium, glucose and amino acids into the cells of the PTC by osmosis.
-This is obligatory water reabsorption- cannot be varied to respond to body’s needs
Renal function: ADH inserts aquaporins into the collecting duct. Why and to what effect ?
-ADH is released from the posterior pituitary gland stimulated by increased osmolarity of ECF or fall in blood pressure e.g. hemorrhage, or blood volume.
- Inserts aquaporins channels into the distal nephron allowing increased absorption of water from the tubule *correction of the initial stimulus.
When stimulates renin secretion and what is the end result of this ?
Two things: the first is a decrease in blood pressure sensed by a loss of stretch in the small arteries feeding the kidney, and the second is reduced sodium concentrations in the distal convoluted tubule (sensed by cells found in the macula densa). The most potent stimulus to renin secretion is both.
How do the kidneys regulate blood pressure and volume?
By removing more or less water.
What is the action of the hormone vasopressin or Antidiuretic hormone?
It causes the kidneys to retain more water by increasing water permeability of the COLLECTING DUCT.
What does it cause the release of Aldosterone in the kidney?
Aldosterone acts on the DISTAL TUBULE a and collecting tubule to increase reabsorption of sodium and calcium
What is Renin?
It is a enzyme created in response to low pressure. It initiates a two step process
1. Angiotensin I
2. hormone Angiotensin II
What does Angiotensin II do?
It increases blood pressure in several ways:
*Vasoconstriction (constricts blood vessels)
*Promotes the release of vasopressin and aldosterone
*Stimulates thirst centers in the brain that encourage water intake
What happens when RBC count drops hypoxia ?
The kidneys that is the regulator (and liver) secretes Erythropoietin to initiate erythropoiesis so erythrocytes are synthesised.
How does calcium homeostasis happens?
1.When there is low calcium in the blood the parathyroid hormone (PTH) is secreted.
2. This stimulates the kidney to produce calcitriol.
What is the action of calcitriol?
It promotes absorption of dietary calcium in the small intestine and increases calcium reabsorption by the kidney.
What is the anatomy of the kidney ?
the Kidney is connected to the ureter which takes urine to the urinary bladder and finally to the urethra.
How does the glomerular capsule ?
Leaky capillaries allow fluid and small molecules through but not cells and proteins. They filtrate about 180 L filtrate that finds its way into the bowman’s capsule.
What are the parts of the nephron?
- glomerulus,
- proximal convoluted tubule,
- loop of Henle,
- distal proximal tubule
How does blood enters and leaves the kidney?
It enters through the renal artery (afferent arteriole) and leaves through the blood vain efferent arteriole.
Where is the blood plasma filtered (general) ?
Blood plasma is filtered through the bowman’s capsule. The filtrate moves through the renal tubule alongside the network of blood capillaries before draining in the collecting duct.
What happens in the PCT proximal convoluted tubule
It is the major site of absorption of sodium(active), magnesium(15-25%), potassium(passive),chloride(passive), calcium. Glucose 100%( active, secondary transport ), Amino Acids 100% (active), Urea (passive). Water by osmosis.
-salts, glucose and amino acids, and that these are mostly actively pumped (requiring ATP) across the wall of the PCT and into the kidney interstitium.
What is reabsorption?
Is when water and solutes within the PCT are transported to the bloodstream.
What happens in the descending and ascending loop of henle
- The loop of Henle allows the establishment of a very salty renal medulla; at 1200 mOsmol it is ~4x the osmolarity of other body tissues (which are ~300 mOsmol).
- The collecting ducts traverse this salty medulla.
The cells here are permeable to water and thus the salt and urea concentration rises within the fluid by the time it reaches the bend. Water leaves by facilitated transport passive
ASCENDING The ascending limb is permeable to sodium chloride, which passes out of the tubule into the medullary tissue surrounding it. ( active transport )
how many nephrons does a kidney has ?
1 million
What happens to the solutes absorbed in the PCT?
Solutes and fluid absorbed into the renal interstitium (ECF) diffuse into blood and so return them to the general circulation. In this way useful substances and water are conserved.
How is glucose absorbed in the PCT ?
glucose is reabsorbed passively by secondary active transport using a created Na+ gradient
The distal tubule function
The distal tubule has the capacity to reabsorb extra Na+ (via aldosterone stimulation) and Ca++ ions (via parathyroid hormone stimulation), depending on the bodies needs.
What would happen in the collecting tube if there are no aquaporins and the duct is IMPERMEABLE to salts and water ?
The the extract would be more diluted because water cannot be reabsorbed into the body creating a diluted urine.
What would happen in the collecting tube if there are aquaporins and the duct is permeable to salts and water ?
- if the walls of the collecting ducts are made permeable to water, then water in the collecting ducts will move (ie diffuse) into the highly osmotic medulla, and the remaining fluid will become concentrated with remaining solutes, producing a concentrated urine.
What is the meaning of diuresis (dehydration)?
refers to the production of a large volume of urine resulting in excretion/loss of body water, the term anti-diuretic becomes obvious.
How does ANTIDIURETIC HORMONE ADH acts in the body ?
acts to insert aquaporins into the membranes of cells lining the collecting ducts. Recall that the collecting ducts pass through the highly salty medulla.
Summary of ADH or vasopressin?
When we are dehydrated, water is reabsorbed from the filtrate in the collecting ducts under the influence of ADH, allowing us to excrete a concentrated, yellow urine. In the absence of ADH, the walls of the collecting ducts are largely impermeable to both salt and water – what arrives at the top is what exits at the bottom, and we produce a dilute urine.
What does ACE stands for ?
It is ANGIOTENSIN- CONVERTING EnZYME It converts the hormone angiotensin I to the active vasoconstrictor angiotensin II.
Is renin an enzyme ?
Yes, it creates a chain reaction designed to regulate your blood pressure. Specifically, renin controls the production of aldosterone, a hormone made by your adrenal glands.
It is located at the juxtaglomerular apparatus.
How might aldosterone increase the salt and water retention ?
increase the amount of salt (sodium) reabsorbed into the bloodstream and to increase the amount of potassium excreted in the urine. Aldosterone also causes water to be reabsorbed along with sodium; this increases blood volume and therefore blood pressure.
reabsorption in the PCT
*Reabsorption is when water and solutes within the PCT are transported into the bloodstream.
*The driving force for the reabsorption in the PCT is sodium.
To create an electrochemical gradient for sodium, Na+-K+-ATPases on the basolateral surface pump out 3 Na+ ions, in exchange for bringing 2 K+ ions into the cell. This transporter uses primary active transport. This movement of Na+ creates an electrochemical gradient favouring the movement of Na+ into the cell from the tubule lumen. WATER FOLLOWS SODIUM, GLUCOSE AND AMINO ACIDS INTO THE CELLS OF THE PCT BY OSMOSIS
* this is an obligatory water reabsorption- cannot be varied to respond to body’s needs
What is the osmolarity of the medulla ?
Henle’s loop is a U-shaped that plays a significant role in maintaining high osmolarity of cortex and medullary interstitial fluid. The osmolarity increases from 300 mOsmolL-1 in the cortex to 1200 mOsmolL-1 in the inner medulla by counter current mechanism. It helps in maintaining the concentration gradient, which in turn helps in easy movement of water from collecting tubules.
Explain the secondary transport of Glucose from the primary filtrate
Potential energy is stored in the electrochemical gradient of Na+ across the cell membrane.
The energy stored in an ion gradient is released when the ion moves down its electrochemical gradient.
Energy can be used to move another substance e.g. glucose, amino acid, against its concentration gradient via a sodium-glucose symporter.
ATP is the indirect source of energy
The osmolarity of the inner cortex medulla ?
1200
Aldosterone in the kidney
increases water intake indirectly and increases sodium intake directly.
What is the role of INTEGRATING centers ?
Complex matters such as blood pressure and thermoregulation requiere control over the heart, blood vessels, fluid balance , salt balance, etc.
RBC
They are called erythrocytes, they are a nuclear red blood cells
Hemoglobin
is an iron containing protein that allows oxygen to be transported to tissue (also co2) from tissue.
What is the difference hypoxia and anoxia
Hypoxic refers to a partial lack of oxygen and anoxic means total lack of oxygen.
How does RBC homeostasis works ?
When the blood oxygen is low Erythropoietin is secreted by the kidneys (and part of the liver).
Erythropoietin initiates erythropoiesis to synthesise erythrocytes .
What would happen to someone in a high altitude?
High altitude= lower atmospheric pressure= low partial pressure (concentration) of oxygen in the extracellular fluids
*Detected by specialized kidney cells which release erythropoietin(EPO)
*EPO acts on the bone marrow to increase the production of red blood cells (erythropoiesis).
*More red blood cells means more capacity to carry oxygen to tissues.
*Increased red cells concentration in the circulation can increase blood viscosity, increasing the risk thrombosis (blood clots)
What is not directly involved in the RBC homeostasis ?
the brain
What is the role of the thyroid and parathyroid glands in calcium homeostasis ?
The thyroid gland secretes calcitonin when plasma calcium rises.
*Parathyroid glands secrete parathyroid hormones when plasma calcium falls-
The hormone that stimulates releases of calcium from bone to increase levels in blood is:
Parathyroidhormone
PTH stimulates
Excretion of phosphate by the kidneys.
Describe the role of insulin in blood glucose regulation. What else does insulin achieve outside the blood glucose control?
Insulin facilitates the removal of glucose from the blood into tissues. allowing it to be used for energy triglycerides converted in storage forms (glycogen or fats)
Insulin acts in insulin receptors to promote facilitated diffusion of glucose into the tissue via glut transporters which are inserted into the plasma membrane.
Insulin is the major “anabolic hormone” which increases protein and patty acids synthesis ( fatty acids are stored in adipocytes as triacylglycerols).
Insulin also reduces production of glucose from glycogen, amino acids or fatty acids.
What are some examples of the importance of calcium ?
Heart contraction, nerve action, blood coagulation and cell division.
Many metabolic roles
What is the main component of hard bone ?
Calcium phosphate
What is the different role of osteoblast vs osteoclast ?
OSTEOCLAST resorb bone to release calcium ( and phosphate inadvertly), while OSTEOBLAST remove calcium from blood to build bone.
What are the feature of calcium homeostasis?
- No control center
-Involves two hormones calcitonin(deposit bone) from the thyroid gland and parathyroid hormone (dissolve bone)from the parathyroid gland.
Why is the release of Ca+ from bone is related to hyperphosphatemia
when dissolving to much bone not only calcim is gained but also phosphate to much phosphate in the bloodstream can create osteoporosis
What are additional roles of phosphate ?
-Activates osteoclasts; calcium and phosphate ions released into the blood.
-Increase calcium absorption from food (intestine)
Promotes activation of vitamin D
In the kidney it increases calcium reabsorption.
What is glycogenolysis and gluconeogenesis?
Glycogenolysis is the breakdown of glycogen occurring in the liver when blood glucose levels drop, whereas gluconeogenesis is the synthesis of glucose from non-carbohydrate sources like lactic acid, glycerol, amino acids and occurs in liver and kidneys.
Why is glucose so important ?
Glucose is a monosaccharide, while the body can utilize a variety of substracts for energy (fats, proteins) the brain requires glucose.
What would happen if a deficit of glucose in the body ?
low blood glucose means low central nervous system activity which can lead to a coma and death and other cells in the body can also starve.
What type of cells secrete insulin and glucagon in the pancreas ?
- Alpha glucagon
-Beta insulin
What is the role of glycogen ?
This stored form of glucose is made up of many connected glucose molecules and is called glycogen. When the body needs a quick boost of energy or when the body isn’t getting glucose from food, glycogen is broken down to release glucose into the bloodstream to be used as fuel for the cells.
How does insulin works ?
Insulin sweeps glucose out of the blood and transforms it into glycogen or fats .
*Insulin acts on insulin receptors to promote facilitates diffusion of glucose into tissue cells. Insulin is the major anabolic hormone
What is the difference between anabolic and catabolic ?
Catabolic breaks down and anabolic unites molecules to transform
What are two homones that can increase blood sugar
Glucagón -alpha cells
Epinephrine, cortisol(adrenal glands , and growth hormone (pituitary)
What is the homeostasis of glucose role of insulin?
-stimulus: rising blood sugar
-beta cells secrete insulin
A.That stimulates gluconeogenesis in the liver (creation of glycogen from glucose)
B. stimulates tissue cells uptake of glucose
-Blood glucose falls to normal range.
How do beta cells sense glucose ?
What kind of transport are the GLUT
the glucose transporter proteins (GLUTs) that transport glucose through facilitative diffusion (a form of passive transport), and sodium-dependent glucose transporters (SGLTs) that use an energy-coupled mechanism (active transport).
How do -beta cells sense glucose
Beta cells has a transporter mechanism lederaded by Glut 2 which takes glucose down its concentration gradient (facilitated diffusion).
1. glucose will go through different reactions. And turned into glucose 6 phosphate (oxidation) to start the glycolysis pathway to produce ATP.
The enzyme that makes this possible is GLUCOKINASE. = pyruvate
2. glucose goes to the mitochondria and starts krebs cycle.
3. This depolarizes the cell to reach -50 mv and the ATP potassium sensitive channels closes.
4. The depolarization opens the calcium channel.
5. Calcium pushes vesicles with insulin to merge with the membrane . Exocitosis
What is Diabetes mellitus ?
It is chronically elevated blood sugar
type I mellitus
Genetic predisposition and response to viral infections seem to initiate autoimmune attack on B cells in pancreas usually occurs on children or adolescents
Type II mellitus
Usually result on poor diet and lack of exercise, possible causes including, down regulation of insulin receptors, insensitivity to insulin
-Chronically elevated glucose [ concentration] appears toxic to beta cells and the release of insulin is decreased
How can exercise can help to overcome type two mellitus?
It increases insulin sensitivity, which helps the cells use any available insulin to take up glucose from the blood.
What are the chronic consequences of diabetes mellitus
Blindness
amputation of lower limbs
kidney failure
impotence
cardiac failure
Blood glucose and glucagon homeostasis
Stimulus- decline blood glucose level
Pancreas is the affector and alpha cells secrete glucagon..
- Glucagon (catabolic)stimulates the breakdown of glycogen into glucose at the liver
-Blood rises to the normal level
the stimulation of initially glycogenolysis and secondly gluconeogenesis
Glycogenolysis:glycogen breaks down into glucose-1-phosphate and glucose
gluconeogenesis: the metabolic process by which organisms produce sugars (namely glucose) for catabolic reactions from non-carbohydrate precursors.
Why does adrenalin increase blood sugar
Since adrenaline gears the body for the fight-or-flight response, it causes a sharp and short-lived increase in blood sugar levels. Adrenaline floods the body with glucose to provide a prompt source of energy to fight or flee the stimulus.
What is diabetes insipidus?
The pituitary gland releases AVP when the amount of water in the body becomes too low.
It helps retain water in the body by reducing the amount of water lost through the kidneys, making the kidney produce more concentrated urine.
In diabetes insipidus, the lack of production of AVP means the kidney cannot make enough concentrated urine and too much water is passed from the body.
What are the causes of diabetes insipidus ?
Neurogenic- insufficient production /release of ADH from the post -pituitary. Often due to hypothalamic tumors, or damage due to head trauma
Nephrogenic- often seen in the end-stage kidney disease, cells no longer receptive to ADH
Psychologigal- vastly increased H2o intake in mentally disabled or health freaks - can drink themselves to death.
Basic physiolog of blood Pressure
*Blood is pumped by the heart ; the increase in heart rate and force of contraction; will rise blood pressure
*Blood is a fluid in tubes : The increase in peripheral resistance will increase blood pressure
*Blood circulates in a closed system; by increasing blood volume the blood pressure will go up
Why is blood pressure crucial ?
oxygen and nutrients would not be pushed around the circulatory system to nourish tissues and organs without blood pressure.
not having blood pressure can produce acute falls.
Blood pressure requires integration of CNS
What are baroreceptors
they are stretch receptors that detect the level of stretch of vascular walls
where are baroreceptors located ?
aortic baroreceptors and carotid baroreceptors
Low-pressure volume receptors, or cardiopulmonary receptors, are located within the atria, ventricles, and pulmonary vasculature
What happens when blood pressures is low ?
the baroreceptors send a signal to the brain in order to activate the sympathetic nervous system to increase blood pressure.
what is hypertension ?
Hypertension is now commonly treated with ACE inhibitors; these inhibit the enzyme (termed angiotensin converting enzyme) which converts inactive angiotensin I to active angiotensin II. definition chronically elevated resting blood pressure,
what are the features of homestasic control mechanisms
- Stressors or change in circumstance, which can be internal or external, lead to either…..
- Stimulus of endocrine glands directly, causing release of “corrective” hormone (or inhibiting release of “causative” hormone)……and/or
- Afferent neural messages from receptors to the integrating CNS, which then….
- Sends efferent neural signals to effectors (either endocrine glands or muscle),
- And the effectors initiate responses to negate the original stressor
What is heat stress
It is heat exhaustion heat-asociated collapse/ discomfort after vigorous exercise or exposure to high environmental temperature
*Elevated core body temperature
*dehydration
* difficulty in maintaining blood pressure
What is heat stroke hyperpyrexia
When core temp exceeds 40 c brain /hypothalamic activity is depressed and thermoregulatory mechanisms work less
How does gain works ?
correction(final value- change before the correction) / errorfinal value- initial set point)
day temperature
The body temperature of a healthy person varies during the day by about 0.5 °C (0.9 °F) with lower temperatures in the morning and higher temperatures in the late afternoon and evening, as the body’s needs and activities change.
what do high concentrations of ADH produce ?
Higher concentrations of anti-diuretic hormone cause blood vessels to constrict (become narrower) and this increases blood pressure.
how do ADH influence pressure
hormone helps to control blood pressure by acting on the kidneys and the blood vessels. Its most important role is to conserve the fluid volume of your body by reducing the amount of water passed out in the urine. It does this by allowing water in the urine to be taken back into the body in a specific area of the kidney. Thus, more water returns to the bloodstream, urine concentration rises and water loss is reduced
