Human Body Systems: Nervous, Excretory, Digestive, Respiratory
Nervous System: Cells
The nervous system is composed of neurons and glial cells. Neurons transmit nerve impulses and do not regenerate. A neuron consists of a cell body, dendrites, and an axon. The space between neurons is called a synapse, where neurotransmitters facilitate communication. Nerve impulses travel from the cell body to the axon.
Types of Neurons:
- Sensory (afferent) neurons: Carry information from receptors to the central nervous system.
- Interneurons: Exist within the central nervous system and communicate between afferent and efferent neurons.
- Motor (efferent) neurons: Carry responses from the central nervous system to muscles, glands, or organs.
Excretory System
Excretion eliminates metabolic waste and toxins. Five pathways include:
- Sweat Glands: Remove sweat to regulate body temperature; cellular debris is excreted through the circulatory system.
- Respiratory System: Excretes carbon dioxide produced during cellular respiration.
- Gastrointestinal System: Eliminates undigested food waste.
- Liver: Removes drug residues and toxins through bile.
- Excretory Organs: Produce urine to remove cellular waste.
Excretory Functions
- Regulates blood pH by managing minerals.
- Controls blood volume by adjusting water retention.
- Removes metabolic waste like urea and uric acid.
The excretory system includes the kidneys and urinary tract. Kidneys filter blood through nephrons. Urine is formed in the nephrons, travels through the renal tubules, and collects in the renal pelvis.
Excretory System Diseases
- Kidney Stones: Formed by precipitated calcium salts due to low water intake.
- Renal Failure: Loss of nephron function, requiring hemodialysis or transplantation.
Digestive System
The digestive system is an irregular tube from mouth to anus, responsible for:
- Transforming food into nutrients.
- Absorbing nutrients into the bloodstream.
- Removing undigested food.
Components
The digestive system includes the gastrointestinal tract and associated glands.
Gastrointestinal Tract
- Mouth: Mechanical (teeth) and chemical (saliva) digestion begin.
- Pharynx: Connects mouth and esophagus; epiglottis prevents food from entering the respiratory tract.
- Esophagus: Transports food to the stomach via peristalsis.
- Stomach: Digests proteins using gastric juices, forming chyme.
- Small Intestine: Duodenum, jejunum, and ileum; completes chemical digestion and absorbs nutrients.
- Large Intestine: Cecum, colon, and anus; absorbs water and minerals.
Associated Glands
- Salivary glands
- Pancreas
- Liver (bile production)
Digestive System Diseases
- Gastric Diseases: Affect the stomach (e.g., gastritis).
- Liver Diseases: Hepatitis, cirrhosis, gallstones.
- Diet-Related Diseases: Constipation, obesity, anorexia, bulimia, deficiency diseases.
Respiratory System
The respiratory system facilitates oxygen uptake for cellular respiration. It consists of:
- Respiratory Tract: Nostrils, pharynx, larynx, trachea, bronchi.
- Lungs: Spongy organs surrounded by pleura; right lung has three lobes, left has two.
Air enters through the nostrils, passes through the pharynx and larynx, enters the trachea, and branches into the bronchi, which lead to alveoli where gas exchange occurs. Breathing involves inspiration (oxygen intake) and expiration (carbon dioxide release), utilizing the diaphragm, intercostal muscles, and rectus abdominis.
Respiratory Diseases
- Infections: Caused by microorganisms (viral or bacterial).
- Pulmonary Emphysema: Destruction of alveolar walls.