Human Biology and Physiology
1. Nutrition and Digestion
a) Devices Involved in Nutrition
The digestive, circulatory, respiratory, and excretory systems are involved in the process of nutrition.
b) Accessory Glands and Secretions
Accessory glands in the digestive system include:
- Salivary glands (saliva)
- Liver (bile)
- Pancreas (enzymes)
2. Mechanical and Chemical Digestion
a) Differences and Importance
Mechanical digestion involves physically breaking down food into smaller pieces, mixing it with digestive juices like saliva, and preparing it for chemical digestion. Chemical digestion uses enzymes to break down the food molecules into nutrients that can be absorbed.
Both processes are essential because they have distinct roles in preparing food for absorption.
b) What is an Enzyme?
An enzyme is a molecule that facilitates chemical digestion.
3. Nutrient Absorption
a) Process and Location
Nutrient absorption is the process of taking in nutrients from food. It primarily occurs in the small intestine, specifically the duodenum and ileum. Specialized structures called villi, with their intricate folds and depressions, increase the surface area for absorption.
b) Ventilation
Ventilation consists of two processes:
- Inspiration (Inhalation): Taking in oxygen. The diaphragm and intercostal muscles contract, expanding the chest cavity and drawing air into the lungs.
- Expiration (Exhalation): Releasing carbon dioxide. The diaphragm and intercostal muscles relax, decreasing the chest cavity volume and expelling air from the lungs.
4. Circulation
a) Double, Closed, and Complete Circulation
Human circulation is double, meaning blood passes through the heart twice in one cycle. It’s closed, meaning blood always stays within vessels. It’s complete, meaning oxygenated and deoxygenated blood don’t mix.
b) Left Ventricle Muscle Mass
The left ventricle is more muscular than the right because it pumps blood to the entire body through the aorta, requiring greater force.
c) Nutrient Transport to Circulation
Nutrients absorbed by the intestine enter the general circulation through the hepatic portal vein.
d) Defining Arteries
Arteries are blood vessels that carry blood away from the heart, regardless of whether the blood is oxygenated or deoxygenated.
5. Circulation and Lymph
a) Pulmonary Circulation
Pulmonary circulation is the flow of blood between the heart and lungs. Deoxygenated blood is pumped from the heart to the lungs, where it picks up oxygen and releases carbon dioxide, then returns to the heart.
b) Lymph
Lymph is a fluid composed of plasma and leukocytes (white blood cells). It plays a role in the immune system and returns excess tissue fluid to the bloodstream. The lymphatic system includes lymph nodes, which are sites where white blood cells accumulate and contribute to immune responses.
6. Excretion
a) Excretory Processes and Locations
- Micturition (Urination): Urethra
- Primary filtration of blood: Renal corpuscle (glomerulus)
- Reabsorption of usable substances: Nephron tubules
- Collecting urine from nephrons: Renal tubules to renal pelvis
- Storage of urine: Bladder
b) Nephron
A nephron is the functional unit of the kidney responsible for filtering blood and producing urine.
c) Urine Formation
Urine is formed through glomerular filtration and tubular reabsorption in the nephron.
8. Nervous System
a) White and Gray Matter
White matter consists primarily of myelinated axons, while gray matter consists of neuronal cell bodies and unmyelinated axons.
In the brain, gray matter is primarily on the outside, while white matter is on the inside. In the spinal cord, white matter is on the outside, and gray matter is on the inside. In the cerebellum, gray matter is on the outside, and white matter is on the inside.
b) Protection of Nerve Centers
- Skull: Protects the brain and brainstem.
- Vertebral column: Protects the spinal cord.
c) Meninges and Cerebrospinal Fluid
The meninges are three protective layers surrounding the central nervous system (CNS): dura mater (outer), arachnoid mater (middle), and pia mater (inner). Cerebrospinal fluid (CSF) is located between the arachnoid and pia mater. The meninges and CSF cushion and protect the CNS.