5.1- communication, homeostasis and energy

Homeostasis

The maintenance of a stable internal environment with restricted limits in organisms

• this ensures that the cells function normally despite changes in the external environment

Why is homeostasis important?

• It keeps the internal environment constant for metabolic reactions.

• It ensures cells function properly and avoid damage.

• It helps organisms respond and adapt to external changes.

receptors

sensory receptors that detect stimuli and send signals to the brain about changes in the internal environment, like changes in blood pH and temperature

coordinator

receives and interprets information from receptors and sends instructions to an appropriate effector

Effectors

A cell, tissue or organism that brings about a response to changes and regain equilibrium

negative feedback

A mechanism that reverses a change bringing a system back to its optimum

How does negative feedback work?

1. Receptors detect a change in one direction, like rising blood glucose.

2. Signals trigger effectors to produce responses that reverse the initial change, like releasing insulin to lower blood glucose.

3. Conditions return to their set range

Positive feedback

Mechanism that increases the change, taking the system further away from the optimum

How does positive feedback work?

1. An initial change occurs, like the release of clotting factors after a blood vessel injury.

2. Effectors are stimulated and enhance the change, like more clotting factors being released.

3. The change continues until an endpoint is met, like a clot being fully formed.

cell signalling

the process by which cells communicate. It can occur between adjacent cells, or between very distant cells.

how does cell signalling occur between cells?

1. Cells can communicate by releasing hormones.

2. These hormones travel in the blood and signal to target cells that may be far away.

3. Cell-surface receptors enable cells to recognise and respond to these hormones.

Excretion

the process of removing metabolic waste from cells

Function of the liver in detoxification

The liver breaks down toxic substances. This process converts these substances into less harmful compounds that cells can excrete

Process of the liver breaking down amino acids

1. Amine groups are removed from amino acids by deamination, producing toxic ammonia and organic acids.

2. Organic acids are either used for ATP production or stored as glycogen.

3. Ammonia combines with CO₂ to form urea via the ornithine cycle, occurring partially in the mitochondria of liver cells.

4. Urea is then excreted from liver cells, enters the bloodstream, and is filtered out of the body via the kidneys as a part of urine.

How is alcohol detoxified?

The enzyme alcohol dehydrogenase breaks down ethanol to ethanal, which is then converted to ethanoate to prevent damage to cells

How is hydrogen peroxide detoxified?

The enzyme catalase splits hydrogen peroxide into oxygen and water to prevent cell damage

Functions of the liver in blood glucose regulation

• Converting excess glucose into glycogen, a storage molecule.

• Storing glycogen granules within its cells.

• Releasing glucose into the bloodstream by breaking down glycogen when blood glucose levels fall.

Function of the liver in breaking down red blood cells

Haemoglobin from old RBCs is broken down in hepatocytes into bile pigments. 

Where are broken down RBCs transported?

excreted from liver cells and transported by the bile duct to the gallbladder where they are stored before their removal from the body

Hepatic artery 

supplies oxygenated blood

Hepatic vein

carries away deoxygenated blood towards the heart

Hepatic portal vein

brings nutrient-rich blood from the intestines

Bile duct

transports bile to the gallbladder

Structure of liver lobules

1. Hepatocytes are arranged along channels called sinusoids

2. The sinusoids are where oxygen-rich blood from the hepatic artery mixes with blood rich in the products of digestion from the hepatic portal vein.

3. A branch of the hepatic vein is located in the centre of each lobule to remove deoxygenated blood.

4. Kupffer cells ingest pathogens and other foreign particles, helping to protect against disease.

5. A channel separate from the sinusoids, called the bile canaliculus, links to a branch of the bile duct.

Where do kidneys receive oxygenated blood?

Through the renal arteries

Where is blood filtered?

in the kidneys?

Function of renal vein

returns filtered blood to the heart via the vena cava

fibrous capsule

An outer membrane that surrounds and protects the kidney

renal cortex

The outer region that contains Bowman's capsules, convoluted tubules, and blood vessels

renal medulla

the inner region with structures called pyramids that contain loops of Henle, collecting ducts, and blood vessels

renal pelvis

The funnel-shaped cavity that collects urine into the ureters

approximately how many nephrons are there in each kidney?

one million

function of nephrons

filter blood, reabsorbing useful substances back into the blood, and removing wastes from the blood

Where is filtrate formed in the nephron?

in the glomerulus

What surround the glomerulus?

The bowman’s capsule, which contains cells called podocytes in its inner layer

What happens in the proximal convoluted tubule?

Useful substances are reabsorbed, including water, glucose, and salts, into surrounding capillaries and the epithelial cells in its wall have microvilli to increase their surface area

Loop of Henle

long, hairpin loop that extends from the cortex into the medulla and then back into the cortex

Function of the loop of henle

It creates a high solute gradient in the medulla, helping with the reabsorption process

function of the distal convoluted tubule

fine-tunes the water balance by reabsorbing water into surrounding capillaries, influenced by antidiuretic hormone

function of collecting duct

collects filtrate from multiple nephrons and further fine-tunes the water balance, before the urine formed is passed to the bladder

Afferent arteriole

supplies the glomerulus with blood

glomerulus

Mass of capillaries in which fluid is forced out of the blood into the Bowman’s capsule through ultrafiltration

efferent arteriole 

carries blood away from the glomerulus

capillaries around the proximal and distal convoluted tubules and the loop of Henle

absorb salts, glucose, and water

ultrafiltration

the process by which small molecules like water, glucose, mineral ions, and urea are filtered out of the blood and into the Bowman's capsule to form glomerular filtrate

where do larger molecules go during ultrafiltration

they remain in the bloodstream

why is ultrafiltration important?

it is essential for filtering blood and maintaining a balance of substances in the body

ultrafiltration process

1. blood enters the glomerulus via afferent arteriole

2. blood leaves glomerulus via efferent arteriole, maintaining a high hydrostatic pressure 

3. the high pressure forces molecules, like water and small solutes, out of the blood via pores in the capillary endothelium

4. molecules move through the basement membrane, which have collagen fibres that act as a selective filter preventing large molecules and blood cells from passing into the bowman’s capsule

5. the molecules move through the bowman’s capsule epithelium, which has specialised cells called podocytes with extensions known as pedicels that wrap around capillaries and help to filter the blood.

6. filtered fluid remains in the bowman’s capsule

glomerular filtrate

The liquid part of blood that enters Bowman’s capsule

glomerular filtration rate

measures the volume of glomerular filtrate formed per minute. it is the volume of blood that is filtered through the kidneys in a given time.

What does the GFR indicate?

how efficiently the kidneys filter blood