EXCRETION Part 2

Dwayne

OSMOREGULATION

Osmoregulation is controlling the amount of water in the blood. The kidney controls the amount of water in the urine/ blood. As the filtrate passes through the nephron water is reabsorbed back into the blood. The amount of water reabsorbed is based on how much water the body needs, The hypothalamus in the brain is responsible for detecting the amount of water in the blood.

 

If there is NOT ENOUGH water in the blood, a hormone called ADH (Antidiuretic hormone) is released from the brain and travels to the kidneys. This is on a hot day when the body loses water in sweat. ADH causes the walls of the nephron to let more water pass back into the blood. So less water passes out in the urine. The urine is concentrated (yellow and has a strong smell).

 

If there is TOO MUCH water in the blood, ADH (Antidiuretic hormone) is NOT released. This is on a cold day or when you drink a lot of water. The walls of the nephron DO NOT allow a lot of water to be reabsorbed back into the blood. So more water passes out in the urine. The urine is dilute (watery and clear).

 

KIDNEY FAILURE

The kidney removes toxic substances from the blood. If the kidney does not clean the blood, the individual will die. When someone is experiencing kidney problems, there are two types of treatment available:

(1)   Dialysis and the artificial kidney

(2)   Kidney Transplant

KIDNEY DIALYSIS

A patient is attached to a kidney dialysis machine. A tube is inserted into the patient’s vein (inside the hand). Blood then passes from the patient into the machine. The machine cleans this blood (removes the urea). The clean blood is then returned to the patient’s hand via another tube. This is done once or twice a week.

 

KIDNEY TRANSPLANT

A healthy person (donor) gives one of his/ her kidneys to the patient (recipient). A surgeon performs the operation.

 

A kidney transplant is better than kidney dialysis. It is cheaper in the long run. The patient can live a normal life (no frequent hospital visits for dialysis).

 

HOW THE BODY LOSES AND GAINS WATER

 

LOSES WATER                                                                    GAINS WATER

Exhaled air                                                                           Food

Sweat                                                                                      Drink

Urine                                                                                       Respiration

Faeces

 

HOMEOSTASIS

Homeostasis is the ability of the body to maintain constant internal conditions despite the external conditions. Homeostasis is controlled by two main systems: NERVOUS and HORMONAL.

 

Examples of Homeostasis:

(1)   Energy levels – when we have little energy left, we consume food. Therefore the energy level in the body is restored to normal.

 

(2)   Body temperature – when the body is too hot, we sweat. This cools us down and normalizes the body temperature. When the body is too cold, we get goose bumps and start to shiver. This warms us up and normalizes the body temperature.

 

(3)   Water levels – if there is too much water in the blood no ADH is released. We urinate more often. If there is not enough water in the blood ADH is released. We urinate less often.

 

(4)   Heart rate and Breathing rate – when we exercise or are anxious or afraid, we breathe faster and the heart beats faster. This allows us to take in more oxygen and to release more carbon dioxide. This allows the heart to pump more oxygen around the body.

 

(5)   Hormone levels – if there is too much glucose in the blood insulin is released. Insulin changes the glucose into glycogen. If there is not enough glucose in the blood glucagon is released. Glucagon changes the glycogen into glucose.

 

 

NEGATIVE FEEDBACK

When a condition in the body changes from the norm, the brain causes the body to change to bring the condition back to normal. For example, if the body temperature increases, sweating cools down the body.

 

THE SKIN AND TEMPERATURE CONTROL

The Skin is the largest and heaviest organ. It is a sense organ that detects touch, temperature, pressure, and pain. It prevents the entry of pathogens. It protects us from the Sun’s harmful UV rays. It excretes urea through sweat. It controls body temperature.

 

COOLING DOWN THE BODY

  • When we are too hot, we sweat a lot. The sweat picks up the heat on the skin. The sweat evaporates from the skin and carries away the heat.
  • Vasodilation – Capillaries get wider and carry more blood to the skin. The blood contains heat which escapes from the surface of the skin.

 

  • The hair on the skin lies flat. There is no layer of air close to the skin. No heat is trapped close to the skin.

WARMING UP THE BODY

  • When we are cold, we do not sweat a lot.

 

  • Vasoconstriction – Capillaries get narrow and less blood flows to the skin.

 

  • The hair on the skin stands straight. There is a layer of air close to the skin. Heat is trapped close to the skin.

 

 

ENDOTHERMS AND ECTOTHERMS

Endotherms are animals that can control their body temperature and keep it constant. Humans control their body temperature so that it is usually around 37oC.

 

Ectotherms are animals that cannot maintain a constant body temperature. Their body temperature varies according to the external temperature. Examples include lizards and fish.

 

EXCRETION IN PLANTS

Waste is excreted through the yellowing leaves of plants. Plants excrete waste gases produced during photosynthesis and respiration.

 

Daytime – Photosynthesis:

CO2 + H2O → glucose + O2

Oxygen exits through the stomata

Nighttime – Respiration:

Glucose + O2 → CO2 + H2O

Carbon dioxide exits through the stomata

 

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