Ch 15 Homeostasis

Question 1

Negative Feedback system

Answer 1

a small change in one direction is detected by sensory receptors. Effectors work to Reverse the Change and restore conditions

Question 2

Positive Feedback System

Answer 2

a Change in the internal environment of the body is Detected by Sensory Receptors, and Effectors are stimulated to Reinforce that Change, Increasing the Response.

Question 3

Ectotherm

Answer 3

“outside heat”
core body temperature is heaviliy dependent on the external environment.
use Behavioural Responses to control body temperature.

Question 4

Endotherms

Answer 4

“inside heat”

organism relies on metabolic processes to maintain a very stable core body temperature, regardless of the environment.

Question 5

Temperature Regulation in Ectotherms

Behavioural Responses:

Answer 5

Bask in sun / Seek shade
orientate body to increase SA exposed
Conduction - press body against warm/cool ground
Maximise/Minimise movement to increase/decrease metabolic heat generated.

Question 6

Temperature Regulation in Ectotherms

Physiological Responses:

Answer 6

Dark colours absorb more radiation than light colours

Alter heart rate to alter metabolic rate

Question 7

Where are Temperature Receptors in Endotherms found?

Answer 7

Peripheral temperature recptors are in the Skin - detect changes in surface temperature. (pre-empt & therefore prevent change in blood temperature)
Temperature Receptors in the Hypothalamus - detect temperature of the blood deep in the body

Question 8

Cooling Down in Endotherms:

Answer 8

Vasodilation
arterioles near skin surface dilate when temp. rises, forcing the blood through the capillary networks at the surface of the skin = skin flushes and cools as a result of increased radiation.
Sweating
rate of sweating increases when core temperature increases. As Sweat Evaporates from the skin surface, heat is lost, cooling the blood bellow.
Erector Pili Muscles Relax
= hair lies flat to avoid trapping insulating layer of air

Question 9

Warming Up in Endotherms:

Answer 9

Vasoconstriction
arterioles near skin surface constrict when temp. falls, so little blood flows through the capillary networks at the surface of the skin = skin looks pale and little radiation takes place. Warm blood is kept well bellow the surafce
Decreased Sweating
rate of sweating decreases/stops as core temperature falls.
Erector Pili Muscles Contract
= Hair/Feathers erect, trapping an insulating layer of air close to skin.
Shivering
= rapid involuntary contracting and relaxing of voluntary muscles. Metabolic heat is produced to raise the core temperature.

Question 10

Temperature Regulation in Endotherms

Anatomical Adaptations:

Answer 10

minimise/maximise surafce are to volume ratio to increase/decrease cooling, e.g. small or large ear.
Thick layer of insulating fat/blubber bellow skin

Question 11

Controlling Thermoregulation:
Heat Loss Centre & Heat Gain Centre

Interaction of Sensory Receptors, Autonomic nervous system, and Effectors in skin & muscles enables Endotherms to maintain a stable core body temperature.

Answer 11

Heat Loss Centre -
activated when Temperature of Blood flowing through Hpothalamus Increases.
Sends impulses through Autonomic Motor Neurones to Effectors in skin & muscles, Triggering Responses to Lower Core Temperature (Cool Down)
Heat Gain Centre -
activated when Temperature of Blood flowing through Hypothalamuc Decreases.
Sends Impulses through Autonomic Motor Neurones to Effectors in skin & muscles, Triggering Responses to Raise Core Temperature (Warm Up)

Question 12

Excretion in Mammal; Main Waste Products:

Answer 12

Carbon Dioxide - waste from cellular respiration, excreted by exhalation out Lungs
Bile Pigments - formed in Liver from Breakdown of Haemoglobin from old red blood cells. Excreted in Bile from Liver into Small Intestine via Gall Bladder & Bile Duct
Nitrogenous Waste Products (Urea) - Formed in Liver from Breakdown of Excess Amino Acids. Urea is Excreted by the Kidneys in the Urine

Question 13

The Liver

Functions:

Answer 13

Reddish-Brown (blood) organ, 5% total body mass
Made of several Lobes
>Hepatic Artery & Hepatic Portal Vein (mix in sinusoids)

Question 14

Structure of the Liver

Answer 14

Hepatocytes -
large nuclei prominant Golgi Apparatus & Lots of Mitochondria
secrete Bile into Canaliculi
Sinusoids = where blood mixes
surrounded by hepatocytes
Kupfer Cells = resident Macrophages, prevent disease

Question 15

Liver : Carbohydrate Metabolism

Answer 15

Blood glucose levels Rise = Insulin levels rise = Hepatocytes convert Glucose into Glycogen (Glycogenesis)
Blood glucose levels Fall = Glucagon levels rise = Hepatocytes convert Glycogen to Glucose (Glycogenolysis)

Question 16

Liver : Deamination of Excess Amino Acids

Answer 16

Deamination = removal of amine group.
convert amino acid into Ammonia (toxic), then to Urea (less toxic), excreted by kidneys
remainder of amino acid fed into cellular respiration or stored as lipid
Ammonia - Urea in Ornithine Cycle; set of enzyme-controlled reactions.
Transamination = conversion of one amino acid into another; important as overcomes problem that diet doesnt always contain required balance of amino acids

Question 17

Liver : Detoxification

& examples

Answer 17

Liver processes toxins, making them harmless
Hydrogen peroxide (catalase) = oxygen and water
Ethanol (alcohol dehydrogenase) = ethanal = ethanoate

Question 18

The Kidneys

Answer 18

Cortex = dark outter layer (capillaries) surrounded by Capsule
Medulla = contains nephron tubules
Pelvis = central chamber where urine collects
>Renal Artery

Question 19

Functional units of the Kidney

Answer 19

Nephrons
blood is filtered = Ultrafiltration
most filtered material returns to blood = Selective Reabsorbtion
Bowman’s Capsule contains Glomerulus - ultrafiltration
Proximal Convoluted Tubule - selective reabsorbtion
Loop of Henle (Descending & Ascending)
Distal Convoluted Tubule - fine tunes salt/water balance
Collecting Duct - fine tuning of salt/water balance (ADH)

Question 20

Process and Structures involved in Ultrafiltration

Answer 20

Relatively wider Afferent arteriole from renal artery supplies blood to glomerulus. Blood leave via narrow Efferent arteriole = Pressue in Arterioles, Forcing blood Out through Capillary Walls (sieve)
Fluid passes through Basement Membrane (network of collagen fibres & other proteins = 2nd sieve)
Podocytes with pedicels (extensions wrap around capillaries forming slits)
Filtrate: glucose, salt, water, urea in same concentrations as blood plasma

Question 21

Selective Reabsorbtion:

Answer 21

water, glucose, salts and other useful substances are returned from filtrate back to blood.
PCT - Glucose, Amino acids, Vitamins & Hormones actively transported back to blood
Sodium ions are actively transported to blood and Chloride ions and Water passively follow down conc gradients.
PCT cells; Microvili increase SA for reabsortion and have many Mitochondira (ATP for active transport)

Question 22

What is the Loop of Henle?

Answer 22

Acts as a Countercurrent Multiplier, using Energy to produce Conc Gradients that Result in Movement of substances such as Water. Ions are actively transported and this produces a Diffusion Gradient in the Medulla.

Question 23

What happens in the Descending Limb of the Loop of Henle?

Answer 23

Filtrate entering is Isotonic with blood
Water diffuses out the filtrate Down W.P gradient by Osmosis.
Upper part is impermeable to water
Lower part is permeable to water
Not permeasble to ions; no active transport
Na+ and Cl- ion concentration in tissue fluid increases in the medulla due to actuvity of the ascending limb.
Fluid reaching hairpin bend is very concentrated and is Hypertonic to the blood in capillaries

Question 24

What happens in the Ascending Limb of the Loop of Henle?

Answer 24

Permeable to Sodium and Chloride ions; Diffuse out Filtrate into blood, Down Concentration gradient.
2nd section of Ascending Limb, Na and Cl ions are actively transported out the filtrate, against a conc gradient. = high concentration of Na and Cl ions in medulla tissue fluid (Essential to Countercurrent Multiplier System)
Impermeable to water (water cannot leave filtrate, so fluid becomes dilute)
fluid at top of Ascending Limb is Hypertonic to blood

Question 25

What happens at the Distal Convoluted Tubule?

Answer 25

Permeability of tubule walls to water depends on ADH.

Cells lining DCT have many mitochondria (ATP for active transport)

Question 26

Collecting Duct

Answer 26

Site where concentration & volume of urine is produced

Permeability of collecting duct to water depends on ADH

Question 27

Osmoregulation

- controlling the water potential of the blood within narrow boundaries

Answer 27

amount of water lost in urine is controlled by ADH in a negative feedback system.
Osmoreceptors in hypothalamus detect low W.P and send nervous impulse to posterior pituitary gland to restore W.P by secreting ADH into bloodstream.
ADH binds to Receptors on cell membrane of Collecting Duct cells, triggering formation of cAMP which causes a cascade of events:
Vesicles in cells lining collecting duct fuse with cell surface membranes
The membranes of these Vesicles contain Aquaporins; protein-based water channels, and when inserted into the cell surface membrane, they make it permeable to water, enabling water to leave the collecting duct and enter tissue fluid then blood by Osmosis.
= W.P of blood increases and small volume of concentrated urine is produced

Question 28

Effects of Kindey Failure

Answer 28

Protein in urine 
Blood in Urine
Loss of Electrolyte balance 
Urea build up in blood
High Blood Pressure

Question 29

Cause of Kidney Failure

Answer 29

Kidney Infection - structure of podocytes is damaged/destroyed
High Blood Pressure
Genetic conditions; e.g. Polycystic Kidney disease

Question 30

Haemodialysis

Answer 30

Dialysis Machine;
Patient’s blood flows into machine and between partially permeable dialysis membranes. On the other side of the membrane is dialysis fluid = concentration gradient for urea and excess mineral ions to diffuse out blood.
Dialysis fluid is carefully controlled and the blood and the Blood and Dialysis Fluid flow in Opposite Directions to maintain a Countercurrent Exchange System to Maximise the Exchange that takes place.

Question 31

Peritoneal Dialysis

Answer 31

Inside body, Diffusion across Peritoneum.
Dialysis Fluid is introduced into the abdomen using a Catheter - Urea and Excess Mineral ions pass out of blood into the dialysis fluid.
Fluid is drained and discarded, leaving the blood balanced.

Question 32

Kidney Transplant

Answer 32

freedom - life without dialysis
Risk of infection
Risk of Rejection- immunosupressant drugs (risk)