Excretion - Chp 31 nf

Excretion

the elimination of metabolic waste from the body

Describe excretion in plants

• stomata and lenticels excrete substances

• during the day oxygen + water vapour are excreted

• during the night carbon dioxide is excreted

What role do excretory organs play in homeostasis?

• regulating body temperature

• controlling osmosis

• controlling the balance of body fluids

• removing waste products

What are the excretory organs of the body + their functions?

• Skin - excretes water and salts, regulates temperature

• Lungs - excrete water vapour and CO₂

• Kidneys - excrete urea, water and salts

Diagram of the skin

Ectotherms

lose or gain heat from their external environment

Endotherms

generate heat from their own metabolic reactions

How does the skin regulate temperature?

When we are cold

• piloerection - the erector muscle attached to each hair follicle contracts pulling the hair upright, this traps a layer of warm air close to the skin

• vasoconstriction - blood vessels in the skin move away from the surface to preserve heat

When we are hot

• hair lies flat on the skin, allowing heat to escape

• vasodilation - The blood vessels expand to move towards the surface of the skin and get rid of excess heat

• sweat - evaporation in a cooling process that takes away the excess heat from the skin

How does skin protect the body?

• Melanin is a brown pigment produced in the cells in the Malpighian layer of the epidermis – this protects from harmful effects of the sun’s rays.

• Keratin is a protein that is produced in the cells of the Granular layer of the epidermis – this creates a waterproof barrier.

• Collagen is a strengthening protein found in the cells of the Dermis – this protects against damage day to day due to its elastic properties.

• Sebum is produced in the sebaceous glands alongside every hair follicle – this protects the hair from damage and stops the skin from cracking and drying up.

What are additional functions of the skin?

• produces vitamin D in the presence of sunlight

• acts as a food and energy store in the adipose tissue

• sensory organ

Overview of the urinary system:

• consists of two kidneys, two ureters, a bladder, a urethra and associated blood vessels

• filtration occurs in the outer cortex of the kidney, resulting the small substances both waste and useful are forced out of the blood

• reabsorption occurs in teh cortex and medulla, allowing useful materials (glucose and amino acids) are taken back into the blood

• secretion occurs in the cortex, and substances such as potassium and hydrogen ions are secreted into the cortex which helps control the blood pH

• once all three processes are complete waste products are collected in the pelvic region and brough into the ureter to go to the bladder for storage

What is the bladder?

• the bladder is a muscular organ that is not under voluntary control

• we have control over the sphincter muscle

• urine is sterile before it leaves the body, once it leaves it is subject to bacterial entities

What are the functions of the kidney?

The kidney has 3 functions:

• Excretion

• Osmoregulation - maintains a balance of salt and water

• pH Control

Diagram of the Nephron

What is the name of the blood vessels that supplies the kidneys with blood?

renal arteries

Describe the blood supply to the Nephron:

• renal artery divides into arterioles

• the afferent arteriole enters the nephron

• it divides further to form a cluster capillaries - the glomerulus

• the glomerulus is located in Bowman’s capsule

• blood leaves the glomerulus through the efferent arteriole

• it divides further into capillaries that surround the rest of the nephron

• capillaries join up to from venules which leave the kidney via the renal vein

Describe the process of filtration:

• blood containing waste enters the glomerulus via the afferent arteriole

• due to high pressure, substances like glucose, amino acids, urea, salts and water are forced out of the glomerulus into the nephron

• this liquid is glomerular filtrate

  • bigger substances like rbcs, wbcs, and platelets do not enter glomerular filtrate

How is the glomerulus adapted for efficient filtration?

• pressure in the glomerulus is higher than normal blood pressure

• there is increased pressure leading into the afferent arteriole

• this leads to ultrafiltration

• there is a large surface area

• walls of the glomerular capillaries are more porous than regular capillaries

Describe the process of reabsorption:

Stage 1 - The Proximal Convoluted Tubule

• the majority of water salts and usefule substances are reabsorbed

• water is reabsorbed by osmosis

• salts and other substances are reabsorbed by diffusion and active transport

Stage 2 - Descending Limb of the Loop of Henle

• more permeable to water

• water is reabsorbed

Stage 3 - Ascending Limb of the Loop of Henle

• more permeable to salt

• salt moves out from the nephron into the medulla of the kidney

  • by diffusion at bottom of the ascending limb

  • by active transport at the top of the ascending limb

• the increase in salt concentration helps remove water from the descending limb and collecting duct

Stage 4 - The Distal Convoluted Tubule

• precisely controls the concentration of water and salt, and pH levels

Stage 5 - The Collecting Duct

• permeable to water, allows a small amount to be reabsorbed

• liquid passing through is urine, and it moves through the ureters into the bladder

How is the proximal convoluted tubule adapted for its purpose?

• it’s long

• it is one cell thick/thin

• it has numerous infoldings to increase surface area

• high concentration of mitochondria provide energy for active transport

Describe Secretion

Hydrogen ions and potassium ions are secreted in the distal tubule to maintain blood pH

What is the difference between glomerular filtrate and urine?

• glomerular filtrate has more water than urine

• glomerular filtrate has useful substances like glucose and amino acids - urine does not

What does ADH stand for + what is another name for it?

ADH - Anti-Diuretic hormone

Vasopressin