Homeostasis in MAMMALS Flashcards
(117 cards)
1
Q
What is homeostasis ?
A
The process of maintaining constant internal body conditions
2
Q
In order to function properly and efficiently what do organisms have?
A
Different control systems that ensure their internal conditions are kept relatively constant
3
Q
Why is homeostasis critically important for organisms ?
A
Ensures the maintenance of optimal conditions for enzyme action and cell function
4
Q
What do sensory cells detect ?
A
Information about the conditions inside and outside of the body
5
Q
What are examples of physiological factors that are controlled by homeostasis in mammals include ?
A
-Core body temperature
- Blood pH
- Concentration of glucose in the blood
-Water potential of the blood
-Concentration of the respiratory gases (carbon dioxide and oxygen) in the blood
6
Q
What do the majority of homeostatic control mechanisms in organisms to maintain homeostatic balance use?
A
Negative feeedback
7
Q
What is homeostatic balance ?
A
To keep certain physiological factors such as blood glucose conc, within certain limits
8
Q
What does a negative feedback control loop involve ?
A
- A receptor (or sensor) – to detect a stimulus that is involved with a condition / physiological factor
A coordination system (nervous system and endocrine system) – to transfer information between different parts of the body
An effector (muscles and glands) – to carry out a response
9
Q
What is the outcome of a negative feedback loop?
A
The factor / stimulus is continuously monitored
If there is an increase in the factor, the body responds to make the factor decrease
If there is a decrease in the factor, the body responds to make the factor increase
10
Q
Homeostasis in mammals relies on 2 diff coordination systems to transfer info between diff parts of the body. What are they?
A
Nervous system – information is transmitted as electrical impulses that travel along neurones
Endocrine system – information is transmitted as chemical messengers called hormones that travel in the blood
11
Q
Define excretion
A
The removal of waste products made from metabolic reactions within the body
12
Q
What are the excretory products formed in humans ?
A
CO2 and urea being formed in much larger quantities than others
13
Q
Where is urea produced ?
A
in the liver from the deamination of excess amino acids
14
Q
If more protein is eaten than is required what happens to the excess?
A
The excess cannot be stored in the body. However the amino acids within the protein can still provide useful energy
15
Q
the amino acids within the protein can still provide useful energy.
To make this energy accessible. What happens?
A
The amino group is removed from each amino acid this process is known as deamination
16
Q
Process of deamination:
A
The amino group (-NH2) of an amino acid is removed, together with an extra hydrogen atom
These combine to form ammonia (NH3)
The remaining keto acid may enter the Krebs cycle to be respired, be converted to glucose, or converted to glycogen / fat for storage
17
Q
Ammonia
A
is a very soluble and highly toxic compound that is produced during deamination; it can be very damaging if allowed to build up in the blood
18
Q
Ammonia is very damaging if allowed to build up in the blood. What happens ?
A
It dissolves in the blood to form alkaline ammonium hydroxide, disrupting blood pH
It can impact the reactions of cell metabolism such as respiration
It interferes with cell signalling processes
This is avoided by converting ammonia to urea
Urea is less soluble and less toxic than ammonia
19
Q
What forms urea?
A
Ammonia combines with CO2
2NH3 + CO2 -> CO(NH2)2 + H2O
20
Q
How many kidneys do humans have?
A
2 kidneys
21
Q
What are the 2 very important functions kidneys responsible for?
A
As an osmoregulatory organ - they regulate the water content of the blood (vital for maintaining blood pressure)
As an excretory organ - they excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts)
22
Q
what is a receptor?
A
A cell or tissue that is sensitive to a specific stimulus and communicates with a control centre by generating nerve impulse or sending a chemical messenger
23
Q
structure of kidney
fibrous capsule
A
The kidney itself is surrounded by a** fairly tough outer layer **
24
Q
beneath the fibrous capsule, the kidney has three main areas. What are they?
A
- The cortex (contains the glomerulus, as well as the Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule of the nephrons)
-The medulla (contains the loop of Henle and collecting duct of the nephrons)
- The renal pelvis (where the ureter joins the kidney)
25
What is the function of the **renal artery**?
carries oxygenated blood (containing urea and salts) to kidneys
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What is the function of the **renal vein**?
carries deoxygenated blood (that has had urea and excess salts removed) away from the kidneys.
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What is the function of the **kidney**?
regulates water content of blood and filters blood
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What is the function of the **Ureter**?
carries urine from kidneys to bladder
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What is the function of the **bladder**?
stores urine (temp)
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What is the function of the **urethra**?
releases urine outside of the body.
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what is a nephron?
- each kidney contains thousands of tiny tubes -> nephrons
- functional unit of kidney
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what is the nephoron resonsible for?
formation of urine
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# part of the network of blood vessels associated with each nephron
Within the Bowman’s capsule of each nephron is a structure known as ?
the **glomerulus**
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Each glomerulus is supplied with blood by?
an **afferent arteriole** (which carries blood from the renal artery)
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The capillaries of the glomerulus rejoin to form an?
efferent arteriole
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Blood then flows from the efferent arteriole into a network of capillaries that run closely alongside the rest of the nephron
Blood from these capillaries eventually flows into the?
renal vein
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what is the 2 stage process called for urine formation in the kidneys?
1. Ultrafiltration
2. Selective reabsorption
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where does Ultrafiltration occur?
in Bowman's capsule
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where does selective reabsorption occur?
Proximal convoluted tube
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what is Ultrafiltration?
small molecules (incl amino acids, water, glucose, urea and inorganic ions) are filtered out of the blood capillaries of the glomerulus and into the Bowmans capsule to from filtrate known as glomerular filtrate
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what is selective reabsorption?
useful molecules are taken back (reabsorbed) from the filtrate and returned to the blood as the filtrate flows along the nephron.
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After the necessary reabsorption of amino acids, water, glucose and inorganic ions is complete (even some urea is reabsorbed) what happens?
the filtrate eventually leaves the nephron and is now referred to as urine
## Footnote
This urine then flows out of the kidneys, along the ureters and into the bladder, where it is temporarily stored
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# ultrafiltration
The capillaries get narrower as they get further into the glomerulus what happens to the blood moving through them?
increases the pressure on the blood
- also already at high pressure as coming directly from renal artery which is connected to the aorta.
44
# ultafiltration
The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them. what does this eventually cause?
the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate
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# ultafiltration
The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by two cell layers with a basement membrane in between them.
what is the first cell layer?
the **endothelium of the capillary** – each capillary endothelial cell is perforated by thousands of tiny membrane-lined circular holes
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# ultafiltration
The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by two cell layers with a basement membrane in between them.
what is the next layer after the endothelium of the cappilary (1st layer)?
**basement membrane** – this is made up of a network of collagen and glycoproteins
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# ultafiltration
The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by two cell layers with a basement membrane in between them.
what is the 2nd layer ?
the **epithelium of the Bowman’s capsule** – these epithelial cells have many tiny finger-like projections with gaps in between them and are known as podocytes
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# ultafiltration
As blood passes through the glomerular capillaries, the holes in the capillary endothelial cells and the gaps between the podocytes allow?
allows substances dissolved in the blood plasma to pass into the Bowman’s capsule
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# ultafiltration
glomerular filtrate
The fluid that filters through from the blood into the Bowman’s capsule
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# ultafiltration
what are the main substances that pass out of the capillaries and form the glomerular filtrate?
amino acids, water, glucose, urea and inorganic ions (mainly Na+, K+ and Cl-)
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# ultafiltration
what remains in the blood ?
**Red and white blood cells and platelets** as they are **too large** to pass through the holes in the capillary endothelial cells
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# ultafiltration
what does the basement membrane acts as?
as a **filter** as it stops large protein molecules from getting through
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How does ultrafiltration occur?
occurs due to the differences in water potential between the plasma in the glomerular capillaries and the filtrate in the Bowman’s capsule
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how does water moved - (to do with water potential) ?
water moves down a water potential gradient, from a region of higher water potential to a region of lower water potential.
Water potential is increased by high pressure and decreased by the presence of solutes
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what are the 2 factors affecting water potential?
pressure and solute concentration
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# factors affecting water potential
How does **pressure** (factor) affects water potential in the glomerulus and the Bowman's capsule?
- As the afferent arteriole is wider than thr efferent arteriole, the blood pressure is relatively high in the glomerular capillaries.
- this raises the water potential of the blood plasma of the blood plasma in the glomerular capillaries above the water potential of the filtrate in the Bowman's capsule.
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pressure -> resulting movement of water
water moves down the water potential grad, from the blood plasma in the glomerular capillaries into the Bowmans capsule.
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# factors affecting water potential
How does **solute concentration** (factor) affects water potential in the glomerulus and the Bowman's capsule?
- whilst the basement membrane allows most solutes within the blood plasma to filter into the Bowman's capsule, plasma protein molecules are too big to get through and stay in the blood
- as a result, the solute conc in the blood plasma in the glomerular capillaries is still higher than that in the filtrate in the Bowman's capsule - this makes the water poteintial of the blood plasma lower than that of the filtrate in the Bowman's capsule
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solute concentration-> resulting movement of water
water moves down water potential grad from the Bowman's capsule into the blood plasma in the glomerular cappilaries
## Footnote
Overall, the effect of the pressure gradient outweighs the effect of solute gradient
Therefore, the water potential of the blood plasma in the glomerulus is higher than the water potential of the filtrate in the Bowman’s capsule
This means that as blood flows through the glomerulus, there is an overall movement of water down the water potential gradient from the blood into the Bowman’s capsule
60
selective reabsorption
Many of the substances that end up in the glomerular filtrate actually need to be kept by the body
These substances are reabsorbed into the blood as the filtrate passes along the nephron
only certain substances are reabsorbed
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where does Glucose reabsorption occur?
in the proximal convoluted tubule
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what is the lining of the proximal convoluted tubule is composed of ?
a single layer of epithelial cells
63
The lining of the proximal convoluted tubule is composed of a single layer of epithelial cells, which are adapted to carry out reabsorption. what are they?
Microvilli
Co-transporter proteins
A high number of mitochondria
Tightly packed cells
64
Water and salts are reabsorbed via ..?
the Loop of Henle and collecting duct
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# Adaptation of proximal convoluted tubule epithelial cell
many microvilli present on the luminal membrane (the cell surface membrane that faces the lumen). How does this adaptation aid reabsorption?
this increases the SA for reabsorption
| SA- surface area
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# Adaptation of proximal convoluted tubule epithelial cell
Many co-transporter proteins in the luminal membrane. How does this adaptation aid reabsorption?
Each type of co-transporter protein transports a specific solute (eg. glucose or a particular amino acid) across the luminal membrane.
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# Adaptation of proximal convoluted tubule epithelial cell
Many mitochondria. How does this adaptation aid reabsorption?
these provide energy for sodium-potassium (Na+ - K+) pump proteins in the basal membranes of the cells.
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# Adaptation of proximal convoluted tubule epithelial cell
cells tightly packed together. How does this adaptation aid reabsorption?
this means that no fluid can pass between the cells (all substances reabsorbed must pass through the cells)
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how selective rabsorption of solutes occurs
- Blood capillaries are located very close to the outer surface of the proximal convoluted tubule
- As the blood in these capillaries comes straight from the glomerulus, it has very little plasma and has lost much of its water, inorganic ions and other small solutes
- The basal membranes (of the proximal convoluted tubule epithelial cells) are the sections of the cell membrane that are closest to the blood capillaries
- Sodium-potassium pumps in these basal membranes move sodium ions out of the epithelial cells and into the blood, where they are carried away
-This lowers the concentration of sodium ions inside the epithelial cells, causing sodium ions in the filtrate to diffuse down their concentration gradient through the luminal membranes (of the epithelial cells)
-These sodium ions do not diffuse freely through the luminal membranes – they must pass through co-transporter proteins in the membrane
- There are several types of these co-transporter proteins – each type transports a sodium ion and another solute from the filtrate (eg. glucose or a particular amino acid)
- Once inside the epithelial cells these solutes diffuse down their concentration gradients, passing through transport proteins in the basal membranes (of the epithelial cells) into the blood
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what are the Molecules that are reabsorbed from the proximal convoluted tubule during selective reabsorption?
**All glucose** in the glomerular filtrate is re-absorbed into the blood
This means no glucose should be present in the urine
**Amino acids, vitamins and inorganic ions** are reabsorbed
The movement of all these solutes from the proximal convoluted tubule into the capillaries increases the water potential of the filtrate and decreases the water potential of the blood in the capillaries
This creates a steep water potential gradient and causes water to move into the blood by osmosis
A significant amount of **urea** is reabsorbed too
The concentration of urea in the filtrate is higher than in the capillaries, causing urea to diffuse from the filtrate back into the blood
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# selective reabsorption
Reabsorption of water and salts
As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion
As salts are reabsorbed back into the blood, water follows by osmosis
Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time
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define osmoregulation
The control of the water potential of body fluids
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what is Osmoregulation a key part of?
homeostasis
74
what are the Specialised sensory neurones known as ?
osmoreceptors
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what do osmoreceptors monitor?
the water potential of the blood (these osmoreceptors are found in an area of the brain known as the hypothalamus)
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If the osmoreceptors detect a decrease in the water potential of the blood what happens?
nerve impulses are sent along these sensory neurones to the posterior pituitary gland (another part of the brain just below the hypothalamus)
These nerve impulses stimulate the posterior pituitary gland to release antidiuretic hormone (ADH)
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where do the ADH molecules enter?
the blood and travel throughout the body
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what does ADH cause?
the kidneys to reabsorb more water
This reduces the loss of water in the urine
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# The effect of ADH on the kidneys
water is reabsorbed by..?
where does the reabsorption occur?
Water is reabsorbed by osmosis from the filtrate in the nephron
This reabsorption occurs as the filtrate passes through structures known as collecting ducts
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# The effect of ADH on the kidneys
ADH causes the luminal membranes (ie. those facing the lumen of the nephron) of the collecting duct cells to become ..?
more permeable to water.
ADH does this by causing an increase in the number of aquaporins (water-permeable channels) in the luminal membranes of the collecting duct cells.
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# The effect of ADH on the kidneys
ADH causes the luminal membranes (ie. those facing the lumen of the nephron) of the collecting duct cells to become more permeable to water.
**describe the following way.**
Collecting duct cells contain vesicles, the membranes of which contain many aquaporins
ADH molecules bind to receptor proteins, activating a signalling cascade that leads to the phosphorylation of the aquaporin molecules
This activates the aquaporins, causing the vesicles to fuse with the luminal membranes of the collecting duct cells
This increases the permeability of the membrane to water
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# The effect of ADH on the kidneys
As the filtrate in the nephron travels along the collecting duct, water molecules move from..?
the collecting duct (high water potential), through the aquaporins, and into the tissue fluid and blood plasma in the medulla (low water potential)
As the filtrate in the collecting duct loses water it becomes more concentrated
As a result, a small volume of concentrated urine is produced. This flows from the kidneys, through the ureters and into the bladder
## Footnote
If the water potential of the blood is too high, the exact opposite happens:
Osmoreceptors in the hypothalamus are not stimulated
No nerve impulses are sent to the posterior pituitary gland
No ADH released
Aquaporins are moved out of the luminal membranes of the collecting duct cells
Collecting duct cells are no longer permeable to water
The filtrate flows along collecting duct but loses no water and is very dilute
A large volume of dilute urine is produced
This flows from the kidneys, through the ureters and into the bladder
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If the concentration of glucose in the blood **decreases** below a certain level....
cells may not have enough glucose for respiration and may not be able to function normally
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If the concentration of glucose in the blood **increases** above a certain level...
this can also disrupt the normal function of cells, potentially causing major problems
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The control of blood glucose concentration is a key part of...
homeostasis
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Blood glucose concentration is controlled by two hormones secreted by endocrine tissue in the pancreas
This tissue is made up of groups of cells known as....
the islets of Langerhans
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The islets of Langerhans contain two cell types:
- α cells that secrete the hormone glucagon
- β cells that secrete the hormone insulin
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The islets of Langerhans contain two cell types:
α cells that secrete the hormone glucagon
β cells that secrete the hormone insulin
**These α and β cells act as**...
the receptors and initiate the response for controlling blood glucose concentration
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The control of blood glucose concentration by glucagon can be used to demonstrate ...
the principles of cell signalling
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Decrease in blood glucose concentration
If a decrease in blood glucose concentration occurs, it is detected by the α and β cells in the pancreas:
The α cells respond by secreting glucagon
The β cells respond by stopping the secretion of insulin
The decrease in blood insulin concentration reduces the use of glucose by liver and muscle cells
Glucagon binds to receptors in the cell surface membranes of liver cells
This binding causes a conformational change in the receptor protein that activates a G protein
This activated G protein activates the enzyme adenylyl cyclase
Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
cAMP binds to protein kinase A enzymes, activating them
Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose
This process is known as glycogenolysis
The enzyme cascade described above amplifies the original signal from glucagon and results in the releasing of extra glucose by the liver to increase the blood glucose concentration back to a normal level
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Increase in blood glucose concentration
When the blood glucose concentration increases to above the normal range it is detected by the β cells in the pancreas
When the concentration of glucose is high glucose molecules enter the β cells by facilitated diffusion
The cells respire this glucose and produce ATP
High concentrations of ATP causes the potassium channels in the β cells to close, producing a change in the membrane potential
This change in the membrane potential causes the voltage-gated calcium channels to open
In response to the influx of calcium ions, the β cells secrete the hormone insulin
Insulin-containing vesicles move towards the cell-surface membrane where they release insulin into the capillaries
Once in the bloodstream, insulin circulates around the body
It stimulates the uptake of glucose by muscles cells, fat cells and the liver
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Insulin increase the uptake of ?
glucose into target cells
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What do The target cells of insulin include?
muscle cells, fat storage cells, adipose tissue and liver cells; all of these cells have specific insulin receptors on their cell surface membranes
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Insulin binds to?
specific receptors on the membranes of these target cells
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The binding of insulin to receptors on target cells stimulates the cells to ?
add more glucose transporter proteins to their cell surface membranes, increasing the permeability of the cells to glucose
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The binding of insulin to receptors on target cells stimulates the cells to add more glucose transporter proteins to their cell surface membranes, increasing the permeability of the cells to glucose
**These glucose transporter proteins are known as?**
GLUT proteins
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When blood glucose levels are low...
GLUT proteins are stored inside the cell in the membranes of vesicles, but when insulin binds to the surface receptors the vesicles move to the cell surface membrane and fuse with it, adding GLUT proteins to the membrane
The rate of facilitated diffusion of glucose into the target cells increases as a result of the increase in GLUT proteins
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Insulin causes activation of an enzyme known as...
glucokinase
99
Glucokinase
phosphorylates glucose, trapping it inside cells
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Insulin causes activation of Glucokinase and another enzyme.. ?
glycogen synthase
101
Glycogen synthase
converts glucose into glycogen in a process known as glycogenesis
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What is Blood glucose concentration regulated by?
negative feedback control mechanisms
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In negative feedback systems:
**Receptors detect** whether a specific level is **too low or too high**
This information is communicated through the **hormonal or nervous system to effectors**
**Effectors** react to counteract the change by **bringing the level back to normal**
104
Negative feedback
In the control of blood glucose concentration:
**α and β cells** in the pancreas act as the **receptors**
They release the hormones glucagon (secreted by α cells) and **insulin** (secreted by β cells)
**Liver cells** act as the **effectors** in response to g**lucagon and liver, muscle and fat cells** act as the **effectors** in response to insulin
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What can People with diabetes not control?
their blood glucose concentration so that it remains within normal, safe limits
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What can act as an indicator that a person may have diabetes?
The presence of glucose in urine
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If blood glucose concentration increases above a value known as the renal threshold....
not all of the glucose from the filtrate in the proximal convoluted tubule is reabsorbed and some will be left in the urine
108
What can be used to test urine for the presence and concentration of glucose?
Test strips
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Two enzymes are immobilised on a small pad at one end of the test strip. These are:
glucose oxidase
peroxidase
The pad is immersed in the urine sample for a short time
110
Two enzymes are immobilised on a small pad at one end of the test strip. These are:
glucose oxidase
peroxidase
The pad is immersed in the urine sample for a short time
**If glucose is present:**
Glucose oxidase catalyses a reaction in which glucose is oxidised to form gluconic acid and hydrogen peroxide
Peroxidase then catalyses a reaction between the hydrogen peroxide and a colourless chemical in the pad to form a brown compound and water
111
What is the colour of the pad is compared to ?
A colour chart
- different colours represent different concentrations of glucose (the higher the concentration of glucose present, the darker the colour)
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What do urine test only show ?
whether or not the blood glucose concentration was above the renal threshold whilst urine was collecting in the bladder – they do not indicate the current blood glucose concentration
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# Measuring blood glucose concentration
who can a biosensor be used by ?
people with diabetes to show their current blood glucose concentration
114
Similar to the test strips, a biosensor uses?
glucose oxidase (but no peroxidase) immobilised on a recognition layer
115
Similar to the test strips, a biosensor uses glucose oxidase (but no peroxidase) immobilised on a recognition layer
**Covering the recognition layer is a**....?
partially permeable membrane that only allows small molecules from the blood to reach the immobilised enzymes
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# Measuring blood glucose conc - biosensor
When a small sample of blood is tested
glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide
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When a small sample of blood is tested, glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide
**The hydrogen peroxide produced is**..?
- oxidised at an electrode that detects electron transfers
- The electron flow is proportional to the glucose concentration of the blood sample
- The biosensor amplifies the current, which is then read by a processor to produce a digital reading for blood glucose concentration
- This process is complete within a matter of seconds
