Physiology Introduce Cells and Homeostasis

Physiology

Physiology

• The word physiology derived from a Greek word for study of nature.

• It is the study of how the body and its partwork or function.

Homeostasis(自稳态)

• Homeostasis is the condition of balance in the body’s internal environment.

Homeostasis

Physiology

Homeostasis

• Although the external environmental changes constantly, the internal environment of a healthy body remains the same with in normal limits.

• Under normal conditions, homeostasis is maintained by adaptive mechanisms ranging from control center in the brain to chemical substances called hormones that are secreted by various organs directly into the blood streams.

• Some of the functions controlled by homeostasis mechanisms are blood pressure, body temperature, breathing and heart rate.

Homeostasis and Body Fluids

• An important aspect of homeostasis is maintaining the volume and composition of body fluids, watery solutions containing dissolved chemicals that are found inside cells as well as surrounding them.

• The fluid within cells is intracellular fluid, (ICF)(细胞内液). The fluid outside body cells is extracellular fluid (ECF)(细胞外液). The ECF that fills the narrow spaces between cells of tissues is known as interstitial fluid(ISF)(组织间液).

Extracellular fluid (ECF)(细胞外液)

ECF differs depending on where it occurs in the body: • The ECF that fills the narrow spaces between cells

of tissues is known as interstitial fluid(ISF)(组织间液). • within blood vessels is termed blood plasma, • within lymphatic vessels it is called lymph, • in and around the brain and spinal cord it is known

as cerebrospinal fluid(CSF), • in joints it is referred to as synovial fluid, and • in the eyes is called aqueous humor and vitreous

body.

Physiology

Control of Homeostasis• The nervous system and the endocrine system,

working together or independently, can usually bring the internal environment back into balance.

• The nervous system regulates homeostasis by sending electrical signals known as nerve impulses (action potentials) to organs.

• The endocrine system includes many glands that secrete hormones into the blood.

• Nerve impulses typically cause rapid changes, but hormones usually work more slowly.

• Both means of regulation, work toward the same end, usually through negative feedback systems.

Physiology

Feedback Systems(反馈系统)

• The body can regulate its internal environment through many feedback systems.

• A feedback system includes three basic components — a receptor(感受器), a control center(中枢), and an effector(效应器).

• A feedback system is a cycle of events in which the status of a body condition is monitored, evaluated, changed, remonitored, reevaluated, and so on.

• Each monitored variable, such as body temperature, blood pressure, or blood glucose level, is termed a controlled condition.

Physiology

Negative & Positive feedback system

• A negative feedback(负反馈) system reverses a change in a controlled condition. Consider the regulation of blood pressure.

• A positive feedback(正反馈) system tends to strengthen or reinforce a change in one of the body’s controlled conditions. Normal childbirth provides a good example of a positive feedback system

Physiology

Negative feedback system

Physiology

Positive feedback system

Physiology

Level of structural organization of the body

• Cell: The smallest independent units of life. • Tissue: tissue is made up of many similar cells that

perform a specific function. • Organ: - Is an integrated collection of two or more

kinds of tissue that works together to perform specific function.

• System: Is a group of organs that work together to perform major function.

• Organism level: - The various organs of the body form the entire organism.

Physiology

Physiology

Cell

• Cell: The smallest independent units of life. – All life depends on the many chemical activities

of cells. – Some of the basic functions of cell are: growth,

metabolism, irritability and reproduction.

Physiology

Parts of Cells

• Plasma Membrane(细胞膜):• Cytoplasm(细胞质)

– Cytosol (细胞液)– Organelles(细胞器)(little organs)

• Nucleus(细胞核)

Parts of CellsPhysiology

Physiology

Plasma Membrane

Plasma membrane is a thin outer membrane, It is a double layered measuring about 4.5 nm and made of phospholipids, cholesterol, glyco-lipid, & carbohydrate.

Functions:1. Separate the cytoplasm inside a cell from extra

cellular fluid.2. Separate cell from one another3. Provide an abundant surface on which chemical

reaction can occur.4. Regulate the passage of materials in to and out of

cells. It also let some things in and keeps others out.

Physiology

Movement across-cell membrane

• Movements a cross membrane takes place in two ways.

• These are passive and active movements. • Passive movement(被动转运) uses its own

kinetic energy(动能） (energy of motion）• Active movement(主动转运) consumes energy in

the form of ATP(Adenosine triphosphate).

Physiology

Passive movementa. Simple diffusion (单纯扩散), the random movements

of molecules from area of high concentration to the area of low concentration. – Example oxygen, carbon dioxide, and nitrogen gases; fatty

acids; steroids; and fat-soluble vitamins (A, D, E, and K). Small, uncharged polar molecules such as water, urea, and small alcohols also pass through the lipid bilayer by simple diffusion.

b. Facilitated diffusion(易化扩散), larger molecules, which are not soluble in lipid need protein channel to pass through the plasma membrane. No direct energy needed. – Example: - Ions (K (potassium ions),Cl (chloride ions), Na

(sodium ions) Ca (calcium ions), glucose, some vitamins, Amino acid passes through the cell membrane.

Physiology

Physiology

Physiology

Active movements

• Substances move through a selectively permeable membrane from areas of low concentration on side of a membrane to an area of higher concentration on the other side.

• This is against concentration gradient.Therefore, it requires energy.

Physiology

Physiology

Phagocytosis（吞噬作用）

• Phagocytosis (吞噬作用）(Cell Eating) is a form of endocytosis(内吞作用)in which the cell engulfs large solid particles, such as worn-out cells, whole bacteria, or viruses.

• Only a few body cells, termed phagocytes(吞噬细胞), are able to carry out phagocytosis.

Physiology

Physiology

Cytoplasm(细胞质)

• Cytoplasm(细胞质) is located between the nucleus and plasma membrane– Cytosol (细胞液), the fluid portion of cytoplasm,

contains water, dissolved solutes, and suspended particles. cytoplasm is the substance that surrounds

– Organelles(细胞器)(little organs). Each type of organelle has a characteristic shape and specific functions.

Physiology

Cytosol• The cytosol (intracellular fluid) is the fluid portion

of the cytoplasm that surrounds organelles and constitutes about 55% of total cell volume. Although it varies in composition and consistency from one part of a cell to another, cytosol is 75–90% water plus various dissolved and suspended components.

• Among these are different types of ions, glucose, amino acids, fatty acids, proteins, lipids, ATP, and waste products.

Physiology

Organelles

Organelles are specialized portion of the cell with a characteristic shape that assume specific role in growth, maintenance, repair and control.

• Golgi Complex(高尔基氏体), near to the nucleus. It consist 4-8 membranous sacs. It process, sort, pack & deliver protein to various parts of the cell.

• Mitochondria(线粒体), a small, spherical, rod shaped or filamentous structure. It generates energy.

• Lysosomes (溶酶体)appear as membrane enclosed spheres. They contain powerful digestive (hydrolytic enzyme capable of breaking down many kinds of molecules.

Nucleus• The nucleus is a oval-shaped structure. It is a large

organelle that houses most of a cell’s DNA. • Within the nucleus, Human somatic (body) cells have

46 chromosomes, 23 inherited from each parent.• a single molecule of DNA (脱氧核糖核酸)

(deoxyribonucleic acid); associated with several proteins, contains thousands of hereditary units called genes(基因) that control most aspects of cellular structure and function.

• Most cells have a single nucleus, although some, such as mature red blood cells, have none. In contrast, skeletal muscle cells and a few other types of cells have multiple nuclei.

Physiology

CELL DIVISION

• Most cells of the human body undergo cell division, the process by which cells reproduce themselves. The two types of cell division—somatic cell division (Mitosis有丝分裂)and reproductive cell division(meiosis减数分裂).

Mitosis有丝分裂

• In somatic cell division, a cell undergoes a nuclear division to produce two identical cells, each with the same number and kind of chromosomes as the original cell.

• Somatic cell division replaces dead or injured cells and adds new ones during tissue growth.

Meiosis (减数分裂)

• Reproductive cell division is the mechanism that produces gametes, the cells needed to form the next generation of sexually reproducing organisms.

• This process consists of a special two step division called meiosis (减数分裂), in which the number of chromosomes in the nucleus is reduced by half.