Page 8 - 84 human physiolofy part-1

Chapter 1

Nervous System

The nervous system, along with the endocrine system, serves as the primary control center of the
body working below the level of consciousness. For example, the hypothalamus of the brain is where
the body's "thermostat" is found. The hypothalamus also stimulates the pituitary gland to release
various hormones that control metabolism and development of the body. The sympathetic and
parasympathetic divisions of the nervous system alternatively stimulate or inhibit various bodily
responses (such as heart rate, breathing rate, etc) to help maintain proper levels. It also controls
contractions like the arrector pili muscles (involved in thermoregulation) and skeletal muscles, which in
addition to moving the body, also cause bone thickening and maintenance, which affects bone
composition. The nervous system also regulates various systems such as respiratory (controls pace and
depth of breathing), cardiovascular system (controls heart rate and blood pressure), endocrine organs
(causes secretion of ADH and oxytocin), the digestive system (regulates the digestive tract movement
and secretion), and the urinary system (it helps adjust renal blood pressure and also controls voiding the
bladder). The nervous system is also involved in our sexual behaviors and functions.

Endocrine System

The endocrine system consists of glands which secrete hormones into the bloodstream. Each
hormone has an effect on one or more target tissues. In this way the endocrine system regulates the
metabolism and development of most body cells and body systems. To be more specific, the Endocrine
system has sex hormones that can activate sebaceous glands, development of mammary glands, alter
dermal blood flow and release lipids from adipocytes and MSH can stimulate melanocytes on our skin.
Our bone growth is regulated by several hormones, and the endocrine system helps with the
mobilization of calcitonin and calcium. In the muscular system hormones adjust muscle metabolism,
energy production, and growth. In the nervous system hormones affect neural metabolism, regulate
fluid/electrolyte balance and help with reproductive hormones that influence CNS development and
behaviors. In the Cardiovascular system we need hormones that regulate the production of RBC's,
elevate and lower blood pressure. Hormones also have anti-inflammatory affects as well as stimulates
the lymphatic system. In summary, the endocrine system has a regulatory effect on basically every
other body system.

Integumentary System

The integumentary system is involved in protecting the body from invading microbes (mainly by
forming a thick impenetrable layer), regulating body temperature through sweating and vasodilation, or
shivering and piloerection (goose bumps), and regulating ion balances in the blood. Stimulation of mast
cells also produce changes in blood flow and capillary permeability which can effect the blood flow in
the body and how it is regulated. It also helps synthesize vitamin D which interacts with calcium and
phosphorus absorption needed for bone growth and maintenance for example if we ever broke a bone
and it needs repair. Hair on the skin guards entrance into the nasal cavity or other orifices preventing
invaders of getting further into our bodies. Our skin also helps maintain balance by excretion of water
and other solutes (i.e.) the keratinized epidermis limits fluid loss through skin. Thus saying it provides
mechanical protection against environmental hazards. We need to remember that our skin is
integumentary, it is our first line of defense and to keep it balanced takes work.

8 | Human Physiology