Homeostasis 

- Homeostasis: The maintenance of a constant internal environment.
- Homeostasis is an automatic process that relies on nerves and hormones without conscious control.

We need to keep the following at constant levels: 
→ Temperature
→ Blood glucose levels.
→ CO₂ levels
→ Water levels

- In general, inputs balance outputs.
- This needs to happen as: 
→ Enzymes control every reaction happening in our cells.
→ Without enzymes, our cells wouldn't function.
→ Homeostasis maintains the ideal conditions at which enzymes work best.

Body Temperature:

- Ideal core body temperature → 37°C (extremities, e.g., fingers and toes, will be colder).
- The optimum temperature for enzymes to function is the ideal core body temperature.
- We can measure temperature using a thermometer, sensitive strips (forehead), and digital probes.
- Thermal imaging uses detection to produce pictures called thermograms.
- Any animal that can maintain a constant body temperature is considered homeothermic or endothermic.

Body Temperature

- Hypothermia: When your body temperature is too low (when the core is below 32°C).
→ When reactions in cells slow down excessively, the pulse rate also slows down, potentially leading to your death.

- Heat Stroke and Dehydration: When your body temperature reaches 40°C or above.
→ Enzymes become damaged/denatured, and you can die.

- 42°C: Death
- 38-39°C: Unusual sweating and fever
- 37°C: Normal body temperature
- 35°C: Shivering
- 33°C: Difficulty in staying awake
- 28°C: Breathing stops
- 25°C: Death

- The brain, particularly the hypothalamus, closely monitors body temperature. When the body temperature deviates from 37°C, the brain activates mechanisms to reverse the change.
→ The brain sends messages to the skin, which are primarily responsible for reversing changes in body temperature.

Heat

- Gaining heat/reducing heat loss in cold conditions:
→ Respiration in cells releases energy as heat.
→ Shivering and exercise (muscles contracting) release heat; muscles need to respire more to contract more.
→ Wearing more clothes helps to insulate the body.

- Vasoconstriction:
→ Wearing more clothes to insulate the body.
→ Going pale—less heat lost by radiation. 

- Losing extra heat in hot conditions:
→ Vasodilation
→ Sweating: The heat from the skin vaporises the water in the sweat, transforming it from liquid to gas.
→ Going red—more heat lost by radiation.
→ Wearing fewer clothes—less insulation.

- Vasoconstriction:
→ They are small arterioles that carry blood to your skin.
→ They become narrower when it's cold, which results in less blood flowing to the skin's surface and less heat loss from radiation.
→Less heat lost by radiation.

Vasodilation:
→ The arterioles that supply blood to the skin widen.
→ More blood to skin surface → more heat lost by radiation.

As soon as you step out of the shower, you feel cold as:
→ Skin is no longer right next to hot water and is exposed to air, which is colder.
→ Sweat, or the heat from your body, evaporates the water on your skin.

- Hypothermia is more likely to happen in an elderly person than in a young, active person. Since young people are more active and generate more heat, they breathe more.
- The body uses negative feedback to maintain its temperature.

Pancreas

The pancreas serves two primary functions:
→ It secretes carbohydrates, proteases, and lipases into the small intestine.
→ It's an endocrine gland; it secretes the hormones insulin and glucagon.

- Insulin and glucagon regulate blood glucose concentration.
- Cells must have a constant supply of glucose to use in respiration to release energy.
- Too much/little glucose in the blood can be extremely dangerous.

Insulin:

- Decreases blood glucose.
- When blood glucose levels are excessively elevated, this substance is released.
- It binds to receptors on cells, particularly in the liver and muscle, to instruct them to take in more glucose.
- Liver and muscle cells can store glucose as glycogen.
→ Glycogen, a large polymer of glucose, is similar to an animal's version of starch.

Glucagon:

- Increases blood glucose.
- It is released when blood glucose levels fall too low.
- It binds to receptors on cells, particularly the liver and muscle, to instruct them to decompose stored glycogen and discharge it into the blood as glucose.

Too Much Glucose:                                                   Glucose: C₆H₁₂O₆

1. Pancreas secretes insulin.
2. This travels in blood to the liver.
3. It stimulates the liver to absorb additional glucose.
4. The liver stores this glucose as glycogen.

Too Little Glucose:

1. Pancreas stops secreting insulin and starts to secrete glucagon.
2. This travels in blood to the liver.
3. It makes the liver break down glycogen into glucose, which enters the blood.

- Blood glucose regulation - negative feedback
- The pancreas is constantly maintaining blood glucose levels.
- Blood glucose levels are maintained at 4-7 mol/dm³.

Diabetes:

- Results in uncontrolled blood glucose levels.
- This condition can lead to poor circulation, damaged nerves, and damaged muscles (feet and legs). In severe cases, amputation may be the only option.
- In extreme cases, people with unoperated diabetes can get kidney failure, fall into a coma, and die.
- There are two types of diabetes.

Diabetes

- 10% of diabetes cases are Type 1.
- The pancreas cannot produce insulin.
- It can occur as an autoimmune condition; white blood cells attack and kill β cells in the pancreas.
- Blood glucose is becoming uncontrollably high (especially after meals).
- Urine excretes excess glucose.
- Cells begin to use fat and protein stores for respiration, resulting in weight loss.
- Eventually, the kidneys may fail, and the person could die.

- 90% of diabetes cases are Type 2.
- Cells stop responding to insulin.
- There's likely a genetic link, as they tend to cluster in families.
- Environmental factors, such as high-sugar diets and sedentary lifestyles, are essential.
- There is a definite connection between type 2 diabetes and obesity.
- Ethnicity plays a factor in how likely you are to get type 2 diabetes, as do genetic and lifestyle differences.
- Even when treated, blood glucose levels cannot reach normal, but concentrations decrease significantly.
- A higher BMI increases the risk of developing type 2 diabetes.
- The older you get, the more likely you are to get type 2 diabetes.
- Women are much more likely to get type 2 diabetes than men.

Testing:

To diagnose type 2 diabetes, use the glucose tolerance test.
1. After the patient has fasted for 8–12 hours, take a blood sample.
2. We administer a high dose of glucose.
3. After two hours, we take another blood sample.
A high glucose reading after 2 hours indicates a person is diabetic.

Symptoms:

- Types 1 and 2 have the same symptoms:
→ Tiredness: Glucose can't enter cells. Therefore, there's no insulin.
→ The kidney excretes glucose from the body frequently.
→ Blurred vision → Glucose builds up in the eye and affects vision.
→ When cells lose weight, they are unable to respire glucose, leading them to respire fat instead.
→ During thirst, the body excretes excess water along with glucose.

- People with diabetes must regularly test their blood using a blood glucose monitor to see how much glucose is in it.

Treatment:

- There is currently no cure.
- Type 1 diabetes is controlled with insulin injections at meal times, as this is when glucose levels will increase.
- Obesity causes Type 2 diabetes in up to 85% of cases, but lifestyle changes (diet and exercise) can control it. They should avoid sugary foods. Exercise helps, as it uses glucose from your meals to respire.

Water Balance

- If we lose too much water, we become dehydrated.
→ A 2% water loss (by body mass) causes extreme thirst.
→ 5-7% → lose ability to work.
→ 10-20% → life-threatening.

- If there's too little water, lysis will occur in body cells.
- If our body cells contain too much water, they will coagulate.
- Osmosis renders both of these unavoidable.

Water loss is unavoidable:
→ Evaporative surfaces constantly lose water.
→ We must excrete urine to remove waste, e.g., urea and excess salts.
→ When the weather is hot, we tend to sweat more.

- Osmoreceptor cells in the hypothalamus constantly monitor the water potential of the blood.
→ These shrink when they become dehydrated.
→ When they shrink, they send impulses to other areas in the brain to induce thirst.
→ They also secrete a hormone called ADH, which travels to the kidney and reduces water loss.

If a person went for a long run, they would experience both gains and losses:
→ More water is made by respiration.
→ More water loss from lungs.
→ More sweat
→ Greater water loss → dehydration

Removing Excess Amino Acids:

- Even when dehydrated, we continue to urinate; therefore, we must remove excretory products and excess ions from our bodies.
- Unlike carbohydrates and fat, we don't store excess amino acids.
→ Excess protein/amino acids in our diet must be excreted.
- The liver absorbs excess amino acids. The liver removes these excess amino groups as ammonia. A process called deamination.
- Since ammonia is toxic, it quickly transforms into urea, a less toxic compound.
- Urea is excreted by kidneys.

Urea:

- Our liver produces this waste product during the breakdown of proteins.
- Urea is toxic because we must dissolve it in water before excreting it.

Kidneys

- Kidneys filter our blood.

- Urine excretes urea, excess water, and salts from the blood.

- The filtering unit of a kidney is a tubule (aka a nephron). It's microscopic.
- The 'filter unit' is the first part of a tubule.
→ The structure consists of a cup-shaped 'Bowman's capsule,' containing a tangle of capillaries known as the glomerulus.
→ Blood enters the glomerulus at high pressure so it can filter quickly.

- During ultrafiltration (at a molecular level—very small), all dissolved molecules are filtered out of the blood and into the Bowman's capsule.
→ Blood filters out substances that are small enough, such as glucose, water, salts, and urea.
→ Things that are too big stay in the blood along with red/white blood cells, antibodies, platelets, and protein.

- The tubule returns beneficial small molecules filtered from the blood to the blood to prevent excretion.
→ The PCT, the first part of the tubule, reabsorbs all glucose and amino acids into the blood.
→ This process, known as selective reabsorption, occurs in the proximal convoluted tubule (PCT).

- The body reabsorbs salts and water in the appropriate amounts.
Urine, the fluid that passes into the urethra, contains urea, uric acid, some salts, and some water.
→ Carried down to the bladder.

- We produce different volumes of urine each day.
- This is affected by:
→ How much you eat/drink
→ How much salt is consumed
→ How much did you exercise?

ADH:

- The pituitary gland secretes ADH in response to low blood water potential.

- ADH travels in the blood to the kidneys and makes tubules more permeable to water.
→ This indicates that the blood absorbs more water.
→ There's less water in urine.

Regulation: Negative feedback example