Homeostasis 🌱

Homeostasis is the maintenance of a stable internal environment in the body. This process includes regulating body temperature (thermoregulation) ❄️🔥, balancing water levels in body fluids (osmoregulation) 💧, maintaining blood sugar levels 🍬, and removing toxic metabolic waste (excretion) 🚮.

Thermoregulation 🌡️

Thermoregulation is the process of maintaining a consistent body temperature, around 37°C in humans, to ensure enzymes operate optimally. Enzymes become less active if the temperature falls below 37°C, and can denature if the temperature rises too high 🔥.

Heat Generation and Loss 🔥❄️

Body heat is primarily generated through metabolic reactions in the liver and muscle shivering. Heat may be lost in the following ways:

• Expiration 🌬️: Heat is lost from the surfaces of the lungs.
• Sweating 💦: Cools the body as sweat evaporates.
• Conduction and Radiation ☀️: Heat is transferred to the environment.
• Excretion and Egestion 🚽: Bodily waste can carry away heat.

The skin, under the control of the hypothalamus in the forebrain 🧠, plays a central role in thermoregulation.

Mechanisms of Thermoregulation by the Skin 🧊🔥

In Cold Temperatures ❄️

To reduce heat loss, the skin adapts through these mechanisms:

• Erector Muscles 💪: Contract to pull hairs upright, trapping a layer of air that insulates against heat loss. Goosebumps form when hair erector muscles contract.
• Vasoconstriction 🩸: Skin arterioles narrow, reducing blood flow near the skin surface and thus limiting heat loss.
• Shunt Vessels 🚧: Open to direct blood away from superficial vessels near the skin surface, reducing heat loss.
• Sweat Glands 💧: Become less active or inactive, minimizing heat loss from sweating.

In Hot Temperatures ☀️

To increase heat loss, the skin responds by:

• Erector Muscles 💨: Relax, causing hairs to lie flat against the skin, which facilitates heat loss through conduction.
• Vasodilation 🩸: Skin arterioles widen, increasing blood flow near the skin surface and allowing more heat to dissipate.
• Shunt Vessels 🚪: Close, directing more blood to superficial vessels and enhancing heat loss.
• Sweat Glands 💦: Become more active, producing more sweat. As sweat evaporates, it absorbs heat and cools the body.

Blood Sugar Regulation 🍭

"Blood sugar" refers to glucose levels in the bloodstream. The pancreas regulates blood sugar using specialized cells called the Islets of Langerhans, which contain two cell types: alpha cells (α-cells) and beta cells (β-cells).

• Alpha Cells 🔼: Secrete glucagon, which raises blood sugar when it is too low.
• Beta Cells 🔽: Secrete insulin, which lowers blood sugar when it is too high.

High Blood Sugar Response 📈

When blood glucose levels rise, the pancreas releases insulin, which reduces glucose levels by:

• Converting excess glucose to glycogen in the liver and muscles (up to 400g can be stored) 🏋️‍♂️.
• Converting excess glucose to fats stored in adipose tissue, particularly around vital organs like the heart ❤️, liver, and kidneys.
• Allowing body cells to absorb and use glucose directly from the blood 🩸.

Diabetes Mellitus occurs when insulin production is insufficient, leading to:

• High blood glucose levels (hyperglycemia) 📈.
• Presence of glucose in urine (glucosuria) 🚽.
• Excessive thirst and water intake 💧.
• Significant weight loss ⚖️.
• Loss of sensation in certain body parts 🦵.

Low Blood Sugar Response 📉

When blood glucose levels are low, the pancreas releases glucagon, which raises glucose levels by:

• Converting glycogen in the liver and muscles back into glucose 🔄.
• Breaking down fats into glucose and, if necessary, modifying proteins for energy production ⚡.