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AL Biology Unit 14 Homeostasis

Follows the AL Biology Syllabus for Cambridge examinations for exams from 2016
by

Blanca Peris

on 27 February 2017

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Transcript of AL Biology Unit 14 Homeostasis

14.5 STRUCTURE OF THE KIDNEY
Animals and plants are complex organisms made up of many millions of cells.
1. Nervous system: in animals the NERVES transfer information as electrical impulses.
14.1 INTERNAL ENVIRONMENT
The internal environment of cells is the
tissue fluid
that bathes them.
http://www.biologymad.com/resources/kidney.swf
WATER POTENTIAL
14.4 EXCRETION
Removal of the unwanted products of metabolism in the body.
14.1 INTERNAL ENVIRONMENT
14.4 EXCRETION
1 DEAMINATION
14.5 STRUCTURE OF THE KIDNEY
1 ULTRAFILTRATION
2 RE-ABSORPTION IN THE PROXIMAL CONVOLUTED TUBULE
3 RE-ABSORPTION IN THE LOOP OF HENLE AND COLLECTING DUCT
4 RE-ABSORPTION IN THE DISTAL CONVOLUTED TUBULE AND COLLECTING DUCT
14.6 CONTROL OF WATER CONTENT
1 OSMORECEPTORS, THE HYPOTHALAMUS AND ADH
2 HOW ADH AFFECTS THE KIDNEYS
3 NEGATIVE FEEDBACK IN THE CONTROL OF WATER CONTENT
14.7 THE CONTROL OF BLOOD GLUCOSE
14.9 HOMEOSTASIS IN PLANTS
1 OPENING AND CLOSING OF STOMATA
2 ABSCISIC ACID AND STOMATAL CLOSURE
1 DEAMINATION
When the liver removes the
nitrogen
from the excess amino acids excreting it in the form of urea and keeping the rest to obtain energy.
keto acid: will be converted to glucose or fat
Ammonia: very soluble and highly toxic
Less soluble and less toxic, excreted
POSSIBLE RESOURCES
Urea is the main NITROGENOUS EXCRETORY PRODUCT of humans, but we also produce small quantities of:
URETER: tube that carries urine from the kidney to the bladder.
The longitudinal section shows that it has 3 main areas:
Structure of a nephron
g: Collecting duct, goes through the medulla until the pelvis and the ureter.
Afferent arteriole (a): branch of the renal artery that supplies blood to the capsule. It forms the glomerulus in the cup of the capsule.
1 ULTRAFILTRATION
3 RE-ABSORPTION IN THE LOOP OF HENLE AND COLLECTING DUCT
4 RE-ABSORPTION IN THE DCT AND COLLECTING DUCT
The kidney makes urine in a two-stage process:
Section glomerulus-renal capsule
The blood in the glomerulus is separated from the lumen of the renal capsule by:
Factors affecting glomerular filtrate.
The fluid filters very quickly thanks to the differences in water potential between the glomerulus and the capsule.
PRESSURE GRADIENT
SOLUTE CONCENTRATION GRADIENT
Inside the glomerulus capillaries the blood pressure is high because the diameter of the afferent arteriole is wider that in the efferent. This raise the water potential of the blood plasma.

2 RE-ABSORPTION IN THE PROXIMAL CONVOLUTED TUBULE (PCT)
Function:
ASCENDING LIMB
Walls permeable to Na+
but impermeable to water
Walls permeable to Na+ and to water
The cells of the walls actively transport Na+ and Cl- ions into the tissue fluid between the two limbs.
DESCENDING LIMB
As the filtrate flows down water goes to the tissue fluid by osmosis.
Na+
Cl-
These limbs side by side enables the maximum concentration inside and outside the tube at the bottom of the loop.
The first part of the DCT behaves like the ascending limb of the loop of Henle.
Desert animals such as kangaroo rats, which need to keep as much water as possible, have especially
long
loops of Henle.
14.6 CONTROL OF WATER CONTENT
1 OSMORECEPTORS, THE HYPOTHALAMUS AND ADH
2 HOW ADH AFFECTS THE KIDNEYS
3 NEGATIVE FEEDBACK IN THE CONTROL OF WATER CONTENT
The kidneys play an important role in homeostasis by the regulation of the concentration of water in the body fluids or
osmoregulation.
What was homeostasis?
When the water content of the blood is low the osmoreceptors stimulate nerve cells in the hypothalamus.
When the nerve cells are stimulated, action potentials (electrical impulses) travel down them.
Diuresis: production of diluted urine
ADH: stops dilute urine being produced.
ADH makes the plasma membrane of the cells in the walls of the collecting duct more permeable to water by increasing the number of water-permeable channels.
MECHANISM
1) ADH molecules bind to receptors in the plasma membrane of the cells from the collecting duct wall.
ADH causes more water to be absorbed.
14.7 THE CONTROL OF BLOOD GLUCOSE
SAQ 18.4
Glucose is transported in solution in the blood plasma.
HIGH LEVELS OF GLUCOSE IN THE BLOOD
After a meal containing carbohydrates they are digested producing glucose that will pass into the blood.
α-cells respond by stopping the secretion of glucagon.
A drop in blood glucose concentration is detected by the α and β cells in the pancreas:
Blood sugar levels never remain constant because there is a time delay between a change in the blood glucose level and the actions to correct it
SAQ 19.7
One of the commonest metabolic diseases in humans. There are two forms:
The symptoms are the same: after they eat a rich carbohydrate meal blood glucose levels rise and stay high.
In type 1 diabetes:
SAQ 19.8
SAQ 19.9
14.6 URINE ANALYSIS
Stages of an action potential:
http://en.wikiversity.org/wiki/File:Action_potential_propagation_animation.gif
Revision Videos
14.9 HOMEOSTASIS IN PLANTS
Plants, like animals, need a constant internal environment.
ABSCISIC ACID AND STOMATAL CLOSURE
Abscisic acid (ABA) is found in every part of the plant.
THE END
Two systems are involved in coordination:
For a proper control every part needs to be coordinated, so connected and informed.
2. Endocryne system: animals and plants use HORMONES, chemical messengers to transfer information.
HOMEOSTASIS: maintenance of a constant internal environment.
Three features need to be kept stable:
WATER IN THE TISSUE FLUID

TEMPERATURE

TEMPERATURE
slow metabolic reactions
proteins denature
CONCENTRATION OF GLUCOSE
GLUCOSE

respiration slows or stops, no energy source
water may go out of the cell by osmosis
TEMPERATURE
GLUCOSE
water goes out from cells by osmosis, then metabolic reactions slow or stop.
too much water entering the cell may cause it to swell or burst.
WATER IN THE TISSUE FLUID
1. Carbon dioxide:
There are two excretory products that are made in large amounts:
2. Urea:
Excreted in the air we breathe out.
Transported to the lungs/alveoli in the blood plasma.
Produced in aerobic respiration.
Excreted dissolved in water as urine.
Transported to the kidneys in solution in blood plasma.
Produced in the LIVER from the excess amino acids.
URIC ACID: made by the break down of nucleic acids.
CREATININE: creatine is made in the liver from certain amino acids.
MEDULLA: central area
CORTEX: beneath the capsule.
CAPSULE: covers the whole structure.
Each kidney receives blood from a RENAL ARTERY and returns blood via RENAL VEIN.
b: Renal (Bowman's) capsule: cup-shaped structure.
(in cortex)
d: Proximal convoluted tubule.
(cortex)
e: loop of Henle,
in the medulla.
f: Distal convoluted tubule, runs back upwards into the
cortex
Blood vessels
Efferent arteriole (c): capillaries of the glomerulus rejoin to form it. Efferent arterioles feed a branch of the renal vein.
2) REABSORPTION: involves taking back any useful molecules from the fluid in the nephron as it flows along.
1) ULTRAFILTRATION: the kidney filters in small molecules, as urea, out of the blood and into the renal capsule. From here they flow along the nephron towards the ureter.
Section glumerulus-renal capsule
The holes in the endothelium and in between podocytes allow the substances dissolved in the blood plasma to get through from the blood into the capsule.
Table 14.1 (p. 308)
Epithelial cells:
inner lining of the renal capsule. They have many tiny finger-like projections and gaps between cells. They are called
PODOCYTES
.
Basement membrane:
made of collagen and glycoproteins. Acts as a FILTER stopping large proteins from getting through (blood cells too large)
Capillary lining or endothelium:
it has thousands of little holes.
Blood plasma and glomerular filtrate are the same except for large plasma proteins
Factors affecting glomerular filtrate.

PRESSURE GRADIENT
SOLUTE CONCENTRATION GRADIENT
Overall, the difference in pressure is higher than in solute concentration so the water potential of the blood plasma in the glomerulus is higher than the liquid inside the capsule.
The concentration of solutes in the blood plasma is higher than in the capsule because of the plasma proteins staying there. This lowers the water potential in the blood capillaries.
So water moves from the blood into the capsule.
2 RE-ABSORPTION IN THE PROXIMAL CONVOLUTED TUBULE (PCT)
WATER
is reabsorbed because as the substances move out of the filtrate water follows by osmosis so the overall concentration of the filtrate remains the same.
Less than the half of the filtrate present in the capsule will arrive to the loop of henle.
Many of the substances in the FILTRATE need to be kept in the body so they are reabsorbed into the blood by
SELECTIVE RE-ABSORPTION
mostly in the PCT.
The uric acid and the creatinine
are not reabsorbed. Creatinine is actively secreted into the lumen.
Urea
is also reabsorbed: it is a small molecule that diffuses passively following the concentration gradient into the blood.
3. There is also a reduction in the filtrate volume.
2. Later this results in water reabsorption in the collecting duct concentrating the urine.
1. Create a very high salt concentration environment in the surrounding tissue fluid in the medulla.
DESCENDING LIMB
Na+
Cl-
Now it flows up the ascending limb, the fluid is so concentrated that Na+ and Cl- diffuse into the tissue fluid.
At the bottom of the tube the fluid has less water and many more ions than in the top, the longer the loop the more concentrated the fluid becomes
Na+ and Cl- ions diffuse into the tube down their concentration gradient.
The fluid continues up becoming less concentrated (but it is still very concentrated)
The degree to which this happens is controlled by the
antidiuretic hormone
(ADH)
Then the fluid goes to the DCT and then to CT (in the medulla).
This mechanism is called a
counter-current multiplier
.
The second part behaves as the collecting duct where Na+ ions are actively pumped to the tissue fluid and K+ ions are actively pumped into the tubule.
What are the elements that make this mechanism work?
What is the mechanism behind homeostasis?
Why do we need to keep constant the water concentration in the tissue fluid?
These cells produce ADH (antidiuretic hormone), a polypeptide that passes along the nerve cells to their endings in the posterior lobe of the pituitary gland.
This releases the ADH to the capillaries in the pituitary gland and then it is carried all over the body.
At the end, with ADH the volume of urine will be smaller and it will be more concentrated. (Fig 14.20)
So as the fluid flows through the collecting duct water moves out of it into tissue fluid down to a concentration gradient because this part of the kidney is very concentrated.
These vesicles contain water-permeable channels so when they fuse they increase the number of these channels.
3) These enzymes cause some vesicles inside the cells to move and fuse with the plasma membrane of the cells.
2) This activates enzymes inside the cells.
a) Flow rate is highest at the beginning of the proximal convoluted tubule, where fluid is entering via filtration into the renal capsule. As the fluid flows along the proximal convoluted tubule, a large percentage of it is reabsorbed,
thus decreasing its volume. There is thus less fluid to fl ow, so less passes a given point in a unit of time; in other words, its flow rate decreases.
This reabsorption continues all along the nephron, which is why the flow rate continues to drop. The rate of fl ow decreases rapidly in the collecting duct, as a high proportion of water may be reabsorbed here.
b) i Glucose concentration drops rapidly to zero as the fluid passes through the proximal convoluted tubule, because all of it is reabsorbed into the blood at this stage.
ii Urea concentration increases because water
is reabsorbed from the tubule.
COORDINATE THE EFFECTORS
β-cells: secrete insulin
α-cells: secrete glucagon
Carried out by the islets of Langerhans, groups of cells scattered throughout the pancreas containing two types of cells:
Very high glucose levels can also cause problems in cells' behaviour.
Some cells such as brain cells can only respire glucose.
If blood glucose levels drops below the normal level (80-120 mg/100 cm3 blood) cells may run short of glucose for RESPIRATION and they will be unable to carry out their normal activities.
For storage, it is converted into GLYCOGEN (polysaccharide, insoluble) stored mostly in the liver and in muscle cells.
HIGH LEVELS OF GLUCOSE IN THE BLOOD
Many cells (liver, muscle, adipose tissue) have insulin receptors.
β-cells respond by secreting insulin into the blood plasma arriving to all parts of the body.
When this glucose flows through the pancreas, α and β cells detect the high levels of glucose:
These processes lower the blood glucose levels.
4 Glucose is converted into glycogen and used in respiration
As a result the liver releases glucose into the blood.
LOW LEVELS OF GLUCOSE IN THE BLOOD
-Production of glucose from fats.
-The use of fatty acids in respiration instead of glucose.
-The breakdown of glycogen to glucose.
Glucagon affects liver cells but muscle cells do not respond to it. Glucagon effects are:
The lack of insulin lowers the rate of glucose absorption by liver and muscle cells.
β-cells respond by stopping the secretion of insulin.
α-cells respond by secreting glucagon.
DIABETES MELLITUS
2) NON-INSULIN-DEPENDENT DIABETES or TYPE 2: the pancreas secretes insulin but the liver and muscle cells do not respond properly to it. It appears late in life and it is often associated with obesity.
1) JUVENIL-ONSET DIABETES or INSULIN-DEPENDENT DIABETES: usually begins early in life.
Between meals, the blood levels of glucose may fall quickly because they do not mobilise glycogen. The lack of glucose for respiration can cause also a coma.
The combination of dehydration, salt loss and low blood pH can cause coma.
They have a very low rate of uptake of glucose into cells so they metabolise fats and proteins producing keto-acids lowering the blood pH.
Extra water and salts pass with this glucose so the person feels very hungry and thirsty.
The kidney cannot reabsorb all the glucose and some passes to the urine.
In type 2 diabetes:
daily blood samples and sugar tests.
The response to the reduction in ADH levels is no immediate.
So the fluid retains more water and dilute urine will be produced.
Then the water-permeable channels are moved again into the cytoplasm.
When the blood water content rises the osmoreceptor are no longer stimulated, stop stimulating nerve cells, so ADH secretion slows down.
Stomata show daily rhythms of opening and closing and they are able to respond to stimuli
E.g. mesophyll cells need a constant supply of carbon dioxide for photosynthesis
Some is converted to creatinine to excrete it and some is used in the muscles.
URETHRA: carries urine to the outside.
Thousands form the kidney
Copy this diagram
2 RE-ABSORPTION IN THE PROXIMAL CONVOLUTED TUBULE (PCT)
SODIUM IONS
: the basal membranes of PCT cells near capillaries transport actively Na+ ions out of the cell so they are reabsorbed in the blood.
Amino acids, vitamins and Cl- ions
: actively reabsorbed.
It uses a special carrier protein that transports Na+ with glucose or other molecule.
This lowers the concentration of Na+ in the cell so they can do facilitated diffusion into the cell down to a concentration gradient from the fluid in the lumen.
GLUCOSE
: transported out of the PCT into the blood, no glucose is present in the urine.
This produces a high concentration of these ions around the descending limb (even 4 times greater)
In the medulla the solute concentration is very high and water potential very low so water moves out the collecting duct by osmosis.
This might be due to a deficiency in the gene which codes for insulin or because of an attack on the
β
cells by person’s own immune system
The pancreas cannot secrete enough insulin.
It stimulates the movement of calcium ions which in turn make K+ to go out of the guard cells.
In stress conditions (drought, high temperatures) causes the stomata to close in a few minutes reducing the water loss from the leaves.
It acts as
stress hormone
.
Water passes out by osmosis so the guard cells become flaccid and close the pore.
14.2 HOMEOSTATIC CONTROL
Most of the control mechanisms in living organisms use a
NEGATIVE FEEDBACK
CONTROL LOOP.
These loops are continuously working keeping the parameter oscillating around a particular ideal level.
It involves a RECEPTOR (aka sensor) and an EFFECTOR (muscles or glands).
14.2 HOMEOSTATIC CONTROL
14.3 THE CONTROL OF BODY TEMPERATURE:
Thermoregulation
14.3 THE CONTROL OF BODY TEMPERATURE
1 DIABETES MELLITUS
14.8 URINE ANALYSIS
1 DIP STICKS AND BIOSENSORS
CHAPTER 14: HOMEOSTASIS
It involves the nervous and endocrine system
Mammals generate heat and have ways to retain it so that they can keep a constant body temperature and be active at any time of day or night.
Heat is generated in respiration, most of it in liver cells as they have a huge requirement for energy.
Then it is absorbed and distributed by the blood.
Central control for body temperature:
HORMONES
NERVES
PAGE 302
Receives input about the temperature of the blood and of the surroundings
PHYSIOLOGICAL RESPONSES TO THE COLD
PHYSIOLOGICAL RESPONSES TO THE HEAT
VASOCONSTRICTION
Muscles in the walls of arterioles that supply blood to capillaries near skin surface contract.
This reduces the supply of blood and less heat is lost
SHIVERING
Involuntary contractions of skeletal muscles produce heat absorbed and distributed by the blood
RAISING BODY HAIRS (no longer useful in humans)
Muscles at the base of hairs in the skin contract to increase the depth of the fur and trap air that acts as insulator.
DECREASING PRODUCTION OF SWEAT
INCREASING SECRETION OF ADRENALINE
It increases the heat production in the liver
This reduces the loss of heat by evaporation from the skin surface
COPY WITH PENCIL
(complete previous diagram)
VASODILATION
Muscles in the walls of arterioles that supply blood to capillaries near skin surface relax.
More heat is lost to the surroundings
LOWERING BODY HAIRS
Muscles at the base of hairs in the skin relax so they lie flat reducing the layer of insulation.
INCREASING SWEAT PRODUCTION
Water evaporates so heat is lost from the skin surface
BEHAVIOURAL RESPONSES: include laying down with the limbs spread out in animals or turning on fans in humans.
NEPHRONS: tiny microscopic tubes, can be seen in a transverse section of the kidney.
RECEPTORS
Insulin also stimulates glucokinase which phosphorylates glucose and it cannot diffuse out.
LOW LEVELS OF GLUCOSE IN THE BLOOD: MECHANISM
5 Glucose will also be produce in gluconeogenesis
STOMATA OPEN
STOMATA CLOSE
Increasing light intensity
Low [CO2] in the air spaces
High [CO2] in the air spaces
Low humidity
High temperature
Water stress: low supply of water from roots or high rate of transpiration.
Darkness
OPENING AND CLOSING THE STOMATA
ABA binds to receptors and inhibits proton pumps to stop the transport of H+ out of guard cells.
If blood glucose concentration increases above the renal threshold not all can be reabsorbed and some will be present in urine.
Protein present in urine may indicate kidney infection or high blood pressure.
DIP STICKS
Can detect glucose, pH, ketones and proteins.
They have the enzyme glucose oxidase, peroxidase and a colourless chemical immobilised on its surface
BIOSENSOR
Size of electrical signal is proportional to the concentration of glucose in the blood.
It has a pad with immobilised glucose oxidase.
The enzyme binds with any glucose in the blood sample producing gluconolactone and a tiny electric current.
This is detected by an electrode and the signal is amplified and read by the meter in seconds.
Each stomatal pore is surrounded by two guard cells that:
CLOSE: when they become flaccid - lose water.
OPEN: when they become turgid - gain water
MECHANISM:
1 Protons are pumped outside the guard cell.
3 Water follows by osmosis
This increases TURGIDITY
2 This causes K+ channels to open. K+ move in as the inside is more negatively charged compared with the outside. (electrochemical gradient)
5 minutes
controlled diet.
regular insulin injections.
most only have a controlled diet.
Ca
2+
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