Homeostasis Shie Yu Hao (22) Per Sheng Xiang (19)

Overall Outline The need for Homeostasis Structure of Mammalian Skin Heat Production and Heat Loss

Small Facts How do they do this? Emperor Penguin, largest of all Penguins, live in Antarctica. These birds breed in extremely low temperature that can drop to -40 degree Celsius. The egg laid by the female is handed over to the male for incubation, and the egg cannot touch the ground or it will freeze immediately! How do they do this?

Homeostasis Definition: Homeostasis is the maintenance of a constant internal environment. Why is there a need for this? Conditions outside our body are constantly changing. Body cells, however, must be kept at constant temperature and bathed in tissue fluid that is kept at a constant pH and water potential.

Constant body temperature Enzymes in our body can only work within certain temperatures. Thus, changes in body temperature too drastically may result in enzyme inactivation or even denaturation. An example will be high fever, that is people suffering from high fever must consult doctors as high fever is highly fatal! Note: Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure.

Constant pH and water potential Drastic change in the pH of tissue fluid will affect enzyme reaction in the tissue cells and harm our body. Composition of tissue fluid must be kept within very narrow limits, thus, any drastic change in water potential will affect our cells. Do you know:  Your kidneys help you regulate the water potential (osmotic pressure) in your blood. When water potential increases, the osmotic pressure of blood will decrease and vice versa.

Homeostatic control of water potential Normal water potential in blood (Norm) Stimulus Water potential of blood decreases (Due to loss of water through profuse perspiration) Receptor (Hypothalamus stimulated) Corrective Mechanism More ADH released by pituitary gland More water reabsorbed by kidney tubules Less water excreted Urine is more concentrated Less urine produced Water potential of blood increases When water potential decreases Negative Feedback

Homeostatic control of water potential Normal water potential in blood (Norm) Stimulus Water potential of blood increases (Due to large intake of water) Receptor (Hypothalamus stimulated) Corrective Mechanism Less ADH released by pituitary gland Less water reabsorbed by kidney tubules More water excreted More dilute urine produced Water potential of blood decreases When water potential increases Negative Feedback

Need for homeostasis Homeostasis is the process that keeps body temperature constant and ensures that the composition of the body fluids is kept within narrow limits. By ensuring a relatively stable internal environment, homeostasis allows an organism: To be independent from changes of external environment. Changes include blood and tissue fluid (mammals).

Homeostasis negative feedback Homeostasis can help you respond to the drastic changes in your body by a receptor (detector). Note: Your body reacts to bring about an opposite effect to changes! Therefore, if the system is disturbed, the disturbance sets in motion a sequence of events that tends to restore the system to its original state. This is the NEGATIVE FEEDBACK process!! Note: A negative feedback response means that your body is gradually going back to normal.

More Facts Organs or Structure that detects changes in body are called receptors/sensors. Changes from normal condition is called stimulus.

Homeostasis Occurrence There must be: A stimulus, change in the internal environment A receptor that detects the stimulus An automatic/self-regulatory corrective mechanism: Brings about reverse effect of stimulus Negative feedback to the receptor

Principle of homeostasis Normal condition or set-point (Norm) Stimulus (Condition rises above normal) Receptor (Detects stimulus) Self-regulatory corrective Mechanism Condition decreases Condition rises Negative Feedback

Principle of homeostasis Normal condition or set-point (Norm) Stimulus (Condition decreases below normal) Receptor (Detects stimulus) Self-regulatory corrective Mechanism Condition increases Condition decreases Negative Feedback

Examples of homeostasis in human Regulating blood glucose concentration Body cells need glucose for tissue respiration Tissue respiration then provides cell with energy for vital activities A drastic change in the blood glucose concentration can be VERY DANGEROUS! Do you know:  Glucose levels in your blood rise after a meal and fall during vigorous exercise or starvation. So, how does our body keep the concentration of glucose in the blood constant?

Blood glucose concentration rises Normal condition or set-point (Norm) Stimulus (Too much glucose in blood ) Receptor (Islets of Langerhans are stimulated) Corrective Mechanism Pancreas secretes more insulin. Causes liver to convert glucose to glycogen Blood glucose concentration falls Negative Feedback

Blood glucose concentration falls Normal condition or set-point (Norm) Stimulus (Too little glucose in blood ) Receptor (Islets of Langerhans are stimulated) Corrective Mechanism Pancreas secretes glucagon Causes liver to convert glycogen to glucose Blood glucose concentration increases Negative Feedback

Structure of mammalian skin Skin forms a protective coat over our body surface Acts as an excretory organ As well as a regulator of body functions So, how does skin do all these stuffs??? Before you can answer this question, you must first learn about the structure of skin 

Structure of mammalian skin Skin is composed of 2 different parts: An outer part called the epidermis An inner thicker part called the dermis

Dermis Upper part of Dermis is thrown into ridges Rich supply of nerves and blood capillaries These structures allow our skin to: Detect changes in the temperature of the surrounding Feel pain E.g. A needle pricks into your skin Blush

Blood vessels in skin A number of blood vessels are present in the dermis Arterioles carries blood to these capillaries Arterioles are controlled by nerves (Vasomotor nerves) Vasomotor nerves brings about reflex contraction and dilation in Arterioles (Vasodilation) When Arterioles dilates, more blood is sent to blood capillaries in your skin Contraction of Arterioles, Vasoconstriction, reduces the amount of blood flowed through the capillaries in the skin (Causing you to become pale) Do you know:  Your skin will turn red when you blush is because of the numerous blood vessels in you skin dilate Contraction and Dilation of you Arterioles help you to regulate body temperature!!!

Hair Hairs are embedded in the dermis, but they are produced by the epidermis. Malpighian layer of the epidermis sinks into the dermis, forming a hollow tube called hair follicle. Each hair grows in a hair follicle. Hair papilla (mass of tissue containing blood capillaries and nerves) are found at the base of the hair follicle. Covered with epidermal cells that constantly divides (Pushes new cells upwards) Cells being pushed upwards soon dies and harden, which form hair 

Hair erector muscles are attached to the hair follicles These muscles can contract, causing: The hairs to “stand on its ends” The skin to be raised around the hair, producing the characteristics “goose pimples” in humans Do you know:  Hair can be specialized for particular purposes. The whiskers or vibrissae of cats and dogs can help them sense objects. The long stiff spines of porcupines are modified hairs used for protection.

Sweat glands Each sweat gland is a coiled tube formed by a down-growth of the epidermis Forms a tight knot in the dermis Richly surrounded by blood capillaries Secreted sweat flows through a sweat duct and a sweat pore to the skin surface Secreted sweat contains mainly water, dissolved salt (sodium chloride) and small amount of urea Sweat contains metabolic waste products such as urea, skin is considered an excretory organ

Sweat secretes continuously Amount of sweat produce, however, varies It may be produced in very small quantities which evaporates almost immediately Or When more sweat is produced, it appears as droplets on your skin or as “running streaks” of liquid in extreme cases Note: Sweat is a mean by which your skin regulates body temperature

Sensory receptors Parts of body that detect changes in the environment or stimuli are called sensory receptors Nerves ending found in the epidermis and dermis are simple sensory receptors Enable us to sense (PPT)- Thermoreceptors: Pain Pressure Temperature changes in the external environment

Sub-cutaneous fat Beneath the dermis are several layers of adipose cells, where fats is stored Fat in these cells also serves as an insulating layer, preventing heat loss

Skin Acts as: A Protective outer covering of the body A Regulatory of body temperature An Excretory organ A Sense organ Skin contains of an outer epidermis and a thick inner dermis In short, JUST REMEMBER: PRESS! 

Heat Production How does your body gain heat? Definition: Heat is produced within you body as a result of metabolic activities such as tissue respiration Lots of tissue respiration takes place in the muscles and liver Thus, large amount of heat are set free in these organs Heat is then distributed to all parts of your body by the blood Do you know:  You can also gain extra heat by eating hot food, exercising, from the sun’s radiation or from warm air on very hot days If these heat is not lost to the surrounding, you may die of overheating

Heat Loss How does your body lose heat? Heat is lost: Through you skin by radiation, convection and to a limited extent, conduction By evaporation of sweat from the surface if your skin In the faeces, urine and in the air that is exhaled Do you know:  Certain parts of your skin contain shunt vessels. These vessels connect the skin arterioles with the venules. They control the amount of blood flowing through your skin capillaries. When shunt vessels constrict, more blood reaches the capillaries in your skin, which increase the amount of heat loss. When shunt vessels dilate to allow more blood to enter them, less blood flows to the capillaries in your skin, thereby decreasing the amount of heat loss. Hence, shunt vessels affect heat loss through skin surface.

Regulating body temperature Hypothalamus in our brain monitors and regulates body temperature Hypothalamus receives information about temperature changes in the external environment from temperature receptors in skin Also monitors temperature of blood passing through it

Human body temperature rises Normal condition or set-point (Norm) Stimulus (Blood and skin temperature increases) Receptor Temperature in skin detects change and send nerve impulses to brain Hypothalamus in brain is stimulated and sends nerve impulses to relevant body parts Corrective Mechanism Arterioles in skin dilate, shunt vessels constrict, more blood flows to blood capillaries in the skin, increasing heat loss Sweat glands more active, more sweat produced, sweat evaporated and more latent heat lost Rapid breathing (helps remove heat) Metabolic rate decreases (decrease heat produced) Blood temperature decreases to the norm Negative Feedback

Human body temperature falls Normal condition or set-point (Norm) Stimulus (Blood and skin temperature decreases) Receptor Temperature in skin detects change and send nerve impulses to brain Hypothalamus in brain is stimulated and sends nerve impulses to relevant body parts Corrective Mechanism Arterioles in skin constrict, shunt vessels dilates, less blood flows to blood capillaries in the skin, decreasing heat loss Sweat glands less active, less sweat produced and less latent heat lost Shiver, if very cold (Contraction of skeletal muscles) Metabolic rate increases (decrease heat produced) Blood temperature increases to the norm Negative Feedback

Results Constant body temperature Extra heat produced is removed at a faster rate so that there is no appreciable rise in body temperature Heat is gained at a faster rate when surrounding temperature drops too low

Thank You !