Human Anatomy and Physiology: Essential Concepts and Systems

Anatomy and Physiology

Anatomy is the branch of biological science that studies the structure, shape, size, location, and relationship of different parts of the human body. It explains how organs, tissues, bones, and systems are arranged. The term is derived from Greek words meaning “to cut apart,” as early studies involved dissecting bodies to understand internal structures.

Branches of Anatomy

• Gross Anatomy: Study of body structures visible to the naked eye (e.g., heart, lungs, bones).
• Microscopic Anatomy: Study of structures requiring a microscope, including cells and tissues.
• Developmental Anatomy: Study of changes in body structure during growth.

Importance of Anatomy

• Helps in understanding body structure.
• Assists in the diagnosis and treatment of diseases.
• Provides essential knowledge for medical and health sciences.

Physiology

Physiology is the branch of biological science that deals with the normal functions and activities of living organisms and their body parts. It explains how organs and systems work together to maintain life.

Branches of Physiology

• Cell Physiology: Study of cell functions.
• Human Physiology: Study of human body functions.
• System Physiology: Study of specific systems like the nervous, cardiovascular, and respiratory systems.

Relationship Between Anatomy and Physiology

Anatomy studies the structure, while physiology studies the function. They are closely related because the structure of an organ determines its function. For example, the heart's specific structure allows it to pump blood effectively.

Cardiac Cycle and ECG

The cardiac cycle is the sequence of events during one complete heartbeat, including contraction (systole) and relaxation (diastole). A normal cycle lasts about 0.8 seconds at 75 beats/minute.

Phases of the Cardiac Cycle

1. Atrial Systole (0.1s): Atria contract, pushing blood into ventricles.
2. Ventricular Systole (0.3s): Ventricles contract, pumping blood into the pulmonary artery and aorta.
3. Complete Cardiac Diastole (0.4s): Both atria and ventricles relax, allowing chambers to fill.

ECG (Electrocardiogram)

An ECG records the heart's electrical activity:

• P Wave: Atrial depolarization (contraction).
• QRS Complex: Ventricular depolarization (contraction).
• T Wave: Ventricular repolarization (relaxation).

Conduction System of the Heart

The conduction system is a specialized network of cardiac muscle cells that generates and transmits electrical impulses to control heart rhythm.

Components

1. Sinoatrial (SA) Node: The natural pacemaker; generates impulses.
2. Atrioventricular (AV) Node: Delays impulses to allow ventricular filling.
3. Bundle of His: Carries impulses to the ventricles.
4. Bundle Branches: Conduct signals down the interventricular septum.
5. Purkinje Fibres: Distribute impulses throughout ventricular muscle.

Regulation of Blood Pressure

Blood pressure (BP) is the force exerted by blood against vessel walls (normal: 120/80 mmHg). It is regulated by:

Short-Term Regulation (Neural)

• Baroreceptor Mechanism: Sensors in carotid arteries and the aorta detect pressure changes and signal the medulla.
• Autonomic Nervous System: Sympathetic nerves increase BP; parasympathetic nerves decrease it.

Long-Term Regulation (Hormonal)

• RAAS: Kidneys release renin, leading to angiotensin II production, which increases BP.
• ADH: Increases water reabsorption.
• ANP: Promotes sodium/water loss to decrease BP.

Vision and Hearing

Physiology of Vision

Light enters through the cornea, is focused by the lens onto the retina, and stimulates photoreceptors (rods for dim light, cones for color). Nerve impulses travel via the optic nerve to the brain.

Physiology of Hearing

Sound waves vibrate the eardrum, move the ear ossicles (malleus, incus, stapes), and stimulate hair cells in the cochlea. These vibrations are converted into electrical impulses sent to the brain.

The Eye: Structure and Function

The eye is a spherical organ consisting of three layers:

• Outer Layer: Sclera (protection) and Cornea (light entry).
• Middle Layer: Choroid (nutrients), Iris (pupil control), and Ciliary Body (lens shape).
• Inner Layer: Retina (photoreceptors).

Peripheral Nervous System (PNS)

The PNS connects the central nervous system to the rest of the body. It is divided into the Somatic (voluntary) and Autonomic (involuntary) nervous systems.

Sympathetic vs. Parasympathetic

• Sympathetic: "Fight or flight"; increases heart rate, dilates pupils, inhibits digestion.
• Parasympathetic: "Rest and digest"; decreases heart rate, constricts pupils, stimulates digestion.

Blood Coagulation (Hemostasis)

Hemostasis prevents excessive blood loss through three stages:

1. Vascular Phase: Vasoconstriction reduces blood flow.
2. Platelet Phase: Platelets form a temporary plug.
3. Coagulation Phase: Clotting factors convert fibrinogen into fibrin, creating a stable clot.

Blood: Composition and Functions

Blood is a fluid connective tissue consisting of:

• Plasma (55%): Water, proteins, salts, and nutrients.
• Formed Elements (45%): RBCs (oxygen transport), WBCs (immunity), and Platelets (clotting).

Physiology of Muscle Contraction

Contraction occurs via the Sliding Filament Theory, where actin and myosin filaments slide over each other. This process requires calcium ions and ATP energy. When nerve impulses stop, calcium is reabsorbed, and the muscle relaxes.

Skeletal System

The skeletal system (206 bones) is divided into:

• Axial Skeleton: Skull, vertebral column, ribs, and sternum.
• Appendicular Skeleton: Limbs and girdles.

Integumentary System (Skin)

The skin consists of the Epidermis (protection), Dermis (nerves/glands), and Hypodermis (insulation). Functions include protection, temperature regulation, sensation, and vitamin D synthesis.

Tissues

Tissues are groups of similar cells performing specific functions:

• Epithelial: Covering and lining.
• Connective: Support and binding.
• Muscular: Movement.
• Nervous: Signal transmission.

Homeostasis and Feedback

Homeostasis maintains a stable internal environment:

• Negative Feedback: Reverses a change (e.g., temperature regulation).
• Positive Feedback: Strengthens a change until a process is complete (e.g., childbirth).

Cell Biology

Transport Mechanisms

Primary Active Transport uses ATP to move substances against a concentration gradient, such as the Sodium-Potassium pump.

Cell Cycle

The cycle includes Interphase (G1, S, G2 growth and DNA replication) and M Phase (Mitosis and Cytokinesis).

Cell Structure

Key organelles include the Nucleus (control center), Mitochondria (energy production), Ribosomes (protein synthesis), and Lysosomes (waste disposal).