HORMONES & HOMEOSTASIS

Hormones

Hormones - Biological chemicals which are synthesized inside your body, which regulate biological systems (ENDOCRINE SYSTEM)

Insulin - Decreases sugar levels by storing sugar as glycogen in muscles.

Glucagon - Increases sugar levels by using sugar stored as glycogen.

Thyroxin - In thyroid gland, it regulates metabolic rate and body temperature.

Leptin - Secreted by adipose tissue*, makes you feel 'full' or 'hungry'

Melatonin - Regulates circadian** cycles. Controlled by light.

Testosterone - Male sex hormone, genitalia, sperm production, aggression etc.

Estrogen & Progesterone - Female sex hormone, reproductive organs, menstrual cycle.

* Adipose Tissue - Where fat is stored (fat cells)

** Circadian cycles - Sleep/wake cycles

*** Secondary Sexual Characteristics - Characteristics which set in after puberty

EXOCRINE SYSTEM - With glands, excreted at place where required

ENDOCRINE SYSTEM - Without glands, directly through circulatory system

Insulin & Glucagon

Body cells need glucose for cellular respiration. Cellular respiration provides cells with energy to perform their vital activities. A drastic change in blood glucose levels thus can be dangerous.

Blood glucose levels should normally be between: 70-90 mg of glucose per cubic cm of blood.

IF BLOOD GLUCOSE IS HIGH IF BLOOD GLUCOSE IS LOW

Blood sugar high

Pancreas secretes insulin

Excess glucose in blood is stored as glycogen in liver

Affects body/liver

HOMEOSTASIS ACHIEVED

Blood sugar low

Pancreas secretes glucagon

Affects body/liver

Glycogen stored in liver is released as glucose into blood

Type 1 Diabetes (Early Onset)

- Strong relationship with genes (hereditary)

- Pancreas cannot produce enough insulin, hence glucose isn't being stored in body, moving in blood

- Beta cells in pancreas destroyed

- Insulin production stops, results in death

- Insulin must be taken externally

Type 2 Diabetes (Adult Onset)

- Hereditary but can be avoided

- Related to stress

- Insulin is being created but cells are desensitized to insulin, hence no effect

- Diet must be controlled

PANCREAS

Alpha cells

Glucagon

Beta Cells

Insulin

Leptin

Melatonin

- Protein hormone

- Controls your diet, inhibits appetite

- More leptin produced, less hungry

- Acts on your hypothalamus through negative feedback

- Pineal glands, controls circadian cycles

- Depends on light, as light increases melatonin decreases,

- High levels cause drowsiness and promotes sleep. Causes drop in core temperature and night body temperature.

Thyroxin

- Thyroid gland, controls metabolism

- Correct functioning of thyroid requires iodine in diet

- Hyper-thyroidism (high metabolism, very thin)

- Hypo-thyroidism (low metabolism, very fat)

- Lack of thyroxin causes lack of energy, depression, weight gain, appetite loss, feeling cold, goitre

Testosterone

- Male hormone (secondary sexual characteristics)

- Pre-natal genitalia, voice deepens, hair everywhere

- Aggression and sex drive 'flight or fight'

- Female hormones (secondary sexual characteristics)

- Menstrual cycle (negative and positive feedback

- Pregnancy differences cycle

*Male and female sex hormones will be discussed in detail in human reproductive system and menstrual cycle topics.

Estrogen & Progesterone

Negative Feedback - Body reacts to bring about an opposite effect to the changes detected from the norm point (e.g. insulin and glucagon in blood glucose).

Positive Feedback - Move away from norm point and bring about greater and greater effect. (e.g. in blood clotting more and more blood clots until the wound is closed)

Adrenaline

- Secreted when you are afraid, angry, anxious or stressed.

- Prepares body for 'fight or flight' mode

- Stimulates liver to convert glycogen to glucose (more energy) and increases blood glucose level

- Increases metabolic rate

- Increases rate of heart beat and causes rise in blood pressure (supply of oxygen to cells of body faster - work more efficiently)

- Increases the rate and depth of ventilation (increases uptake of oxygen)

- Increases rate of blood clotting

- Constricts artrioles to gut, decreasing digestive activities

- Constricts artrioles to skin, causing paleness

- Blood channelled to muscles

- Dilates pupils to enhance vision

- Contracts hair muscles, creating goose bumps and causing hair to stand on end

Figure 2. Difference between endocrine and nervous system

Figure 1. Location of hormone glands

Homeostasis

Monitoring levels of variability, makes correction by negative and positive feedback mechanisms; maintenance of a constant internal environment.

Endocrine System - Composed of certain glands which secrete chemicals (into circulatory system). Those chemicals are known as hormones, which work together with the nervous system to obtain homeostasis.

MONITOR EVALUATE ADJUST

Sensory neurons Control center Effectors

Regulating Blood Water Potential

Water potential increases:

- Less ADH (anti-deuretic hormone) released by pituitary gland

- Less ADH transported to kidneys

- Cells in the walls of collecting ducts become less permeable to water

- Less water reabsorbed into bloodstream

- Urine is more dilute and greater in volume

Water potential decreases:

- More ADH released by pituitary gland

- More ADH transported to kidneys

- Cells in the walls of collecting ducts become more permeable to water

- More water reabsorbed into bloodstream

- Urine is more concentrated and less in volume

Temperature regulation & Skin

Skin is composed of 2 parts - an outer part called the epidermis and an inner thicker part called the dermis. The dermis has a rich supply of nerves and blood capillaries.

Blood vessels in the dermis layer and involved in temperature regulation in the skin. The constriction and dilation of arterioles helps to regulate your body temperature.

Dilation of the arterioles is called vasodilation. When the skin arterioles dilate, more blood is sent to the blood capillaries in your skin.

Constriction of the arterioles is called vasoconstriction. When the skin arterioles constrict, the amount of blood flowing through blood capillaries in your skin decreases.

Hair erector muscles are attached to the hair follicles present in the skin. When these muscles contract, the hair stands on their ends and skin around the hair is raised resulting in goose pimples.

Each sweat gland is a coiled tube formed by a downgrowth of the epidermis. It forms a tight knot in the dermis and is surrounded by many blood capillaries. Secreted sweat flows through a sweat duct to a sweat pore that opens at the skin surface. Secreted sweat mainly contains water, dissolved salts and small amounts of urea.

Adipose tissues are stored underneath the skin. Since adipose tissue is where fat is stored - and fat is an insulating material - the layer of adipose tissue acts as an insulating layer and heat loss is reduced.

Figure 3. Osmo-regulation & ADH

How does your body produce & gain heat?

- Heat produced as a result of metabolic activities taking place inside body

- Vigorous muscular exercise

- Consumption of hot food

- Being in warm environments

How does your body lose heat?

- Through skin by radiation, convection and conduction

- By evaporation of water in sweat from the surface of your skin

- In faeces and urine

- In the air that is exhaled

Regulating body temperature

- The hypothalamus monitors and controls body temp.

- The hypothalamus receives information about the temp through:

- Thermoreceptors in the skin (temp of environment)

- Thermoreceptors in the hypothalamus (temp of blood)

Figure 4. Skin cell

Figure 12.5 Vasoconstriction Figure 12.6 Vasodilation

Hot temperatures

VASODILATION - Dilation of arterioles in skin and constriction of shunt vessels allow more blood to flow through blood capillaries in your skin. This allows more heat to be lost through your skin by radiation, convection and conduction.
MORE SWEATING - Sweat glands become more active, resulting in increased production of sweat. As more water in the sweat evaporates from the surface of your skin, more latent heat of vaporization is lost from your body.
DECREASED METABOLIC RATE - To reduce the amount of heat being released within your body.

Cold temperatures

VASOCONSTRICTION - Constriction of arterioles in skin and dilation of shunt vessels so that less blood flows through blood capillaries in your skin. This reduces the heat lost through your skin by radiation, convection and conduction.
LESS SWEATING - Sweat glands become less active, resulting in decreased production of sweat. As less water in the sweat evaporates from the surface of your skin, less latent heat of vaporization is lost from your body
INCREASED METABOLIC RATE - To increase the amount of heat being released within your body.
SHIVERING - When the above reactions are not sufficient to prevent a drop in body temperature, ‘shivering’, a reflex contraction of your body muscles occurs. This reaction increases the heat being released by muscles and helps raise body temperature.