What has happened to these people?

How did people understand unusual diseases in the old days ? Witch craft Punishment from God

How do scientists understand diseases?

Definition: Keeping the internal environment in a Steady state It is controlled by Negative Feedback Mechanism

Homeostatic control system The body can regulate its internal environment through a multitude of feedback systems A feedback system is a cycle of events in which the status of body condition is continually monitored, evaluated, changed, re-monitored, re-evaluated and so on. Any disruption that changes a controlled condition is called a stimulus

Three basic components RECEPTOR CONTROL SYSTEM EFFECTOR

RECEPTOR a body structure that monitors changes in a controlled condition and sends input in the form of nerve impulses or chemical signals to a control center. CONTROL SYSTEM evaluates the input it receives from receptors and generates output commands when they are needed. output from the control center can occur in several forms: nerve impulses, hormones, or other chemical signal

EFFECTOR is a body structure that receives output from the control centre and produces a response or effect that changes the controlled condition. either depressing it (negative feedback) or enhancing it (positive feedback)

Feedback System Negative feedback Homeostatic mechanism that reduces the intensity of the original stimulus Consequently causes a change in a variable that is opposite in direction to the initial change Positive feedback A feedback mechanism in which the response enhances the original stimulus

Rise above normal value Fall below normal value Corrective Mechanism NEGATIVE FEEDBACK MECHANISM normal value negative feedback

Parts of Body involved kidneys : regulate water & mineral salts concentration skin : regulate body temperature liver & pancreas : regulate blood glucose level Excretory system kidney liver pancreas + skin tissue cells blood

Osmoregulation (Water & Mineral salts) Regulate water potential in Tissue Fluid Organ involved: KIDNEYs System involved : Urinary system

Normal Water Content in Blood After Sweating Concentrated Blood Larger proportion of water is reabsorbed Concentrated Urine is produced

Normal Water Content in Blood After Drinking Diluted Blood Smaller proportion of water is reabsorbed Diluted Urine is produced

Osmoregulation (Water & Mineral salts) After having a very salty meal  produce concentrated urine to remove excess salts in solution form  extra water is needed to be excreted along with the excess salts  sensation of thirst (drink more water to compensate for the water loss)

Thermoregulation (Regulation of Body Temperature) Cold-blooded animals body temperatures vary with that of the environment e.g. reptiles, fish, amphibians

Thermoregulation (Regulation of Body Temperature) Warm-blooded animals keep body temperature constant even in winter by increasing metabolic rate e.g. birds, mammals

Maintenance of Body Temperature

Epidermis Dermis Outermost layer Middle layer Innermost layer Sweat gland Blood capillaries Subcutaneous fat Receptors Erector muscle Nerve fibres Sebaceous gland Hair follicle Structure of Mammalian Skin

Functions of Our Skin  protect the body (epidermis)  to provide mechanical protection  to prevent bacterial entry  to reduce water loss  temperature regulation (hair)

Functions of Our Skin  excretion of sweat (sweat gland)  store fats (subcutaneous fat)  sensation (numerous receptors )  production of vitamin D under ultra-violet light (inner epidermis)

Control Body Temperature in Hot Conditions

 More sweat is produced by sweat glands evaporation of sweat takes away heat which produces a cooling effect  Vasodilation of skin arterioles arterioles near the surface of the skin dilates to let more blood flows near the skin surface to have more heat lost by conduction & radiation.

 Muscles relax hairs lie flat on the skin reduce thickness of air trapped among the hairs (not effective in human because human’s hairs are short)

 Develop thinner fat & shed their fur as long term responses increase heat loss  Decrease metabolic rate & muscle contraction gain less heat

Control Body Temperature in Cold Conditions

 Vasoconstriction of skin arterioles arterioles near the surface of the skin constrict to let less blood flows near the skin surface to have less heat lost by conduction & radiation

 Muscles contract pull hairs for trapping more air thicker layer of air acts as a good insulator of heat  Less sweat is produced by sweat glands reduce heat loss by evaporation

 Develop thicker fat & thicker fur as long term responses reduce heat loss  Increase metabolic rate & muscle contraction gain more heat

Nervous system

Regulation of Blood Glucose Level  controlled by Negative feedback mechanism  controlled by insulin secreted from the islets of Langerhans in pancreas  Diabetes - malfunction of pancreas (does not secrete enough insulin)  Digestive system

Liver converts glycogen to glucose normal blood glucose level Blood glucose level falls Soon after a meal Long after a meal Blood glucose level rises normal blood glucose level Too High Too Low Pancreas secretes insulin Pancreas secretes less insulin Liver coverts glucose to glycogen