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