Human Biology and Nutrition
Sense Organs
Hearing
Hearing consists of three parts: the external ear, middle ear, and inner ear.
External Ear
This is formed by the pinna, the ear canal, and the eardrum.
- It is in charge of collecting and transmitting sound waves into the middle ear.
- The ear canal contains small hairs and wax-producing glands that are responsible for protecting the inside.
- The eardrum is a membrane that separates the outer ear and middle ear.
Middle Ear
This is formed by the tympanic cavity, which contains three holes.
- One hole is closed toward the exterior.
- The other two holes are on the eardrum inwards, called the oval window and round window.
- There is a channel that communicates with the Eustachian tube and pharynx, which is responsible for balancing the atmospheric pressure on both sides.
- The ossicular chain (hammer, anvil, and stirrup) is responsible for sending sound waves into the inner ear amplified.
Inner Ear
It is divided into two chambers filled with a fluid called endolymph.
- One chamber is called the utricle, and the other is called the saccule.
- The saccule contains a spiral-shaped channel called the cochlea.
- When sound reaches the inner ear, the endolymph moves and fills the cochlea, stimulating the sensory cells connected to the auditory nerve.
- Sensitive cells located in the semicircular canals are responsible for the sense of equilibrium.
Eye Structure
The eye consists of three layers from outside to inside: the sclera, choroid, and retina.
Sclera
- An opaque whitish layer that looks hard.
- At the front of the eye, it has a convex area called the cornea.
- The cornea is transparent and allows light to enter.
Choroid
- Situated beneath the sclera and is black.
- In front of the eye, it forms a disc called the iris.
- The iris is a muscle responsible for the coloration of the eye.
- At the center of the iris is the pupil, a hole that controls the entry of light.
Retina
- The innermost layer.
- It contains the receptor cells of vision.
- There are two types of receptor cells: rods, which give us black and white coloration, and cones, which give us color vision.
The three layers converge at a point where they exit into the optic nerve. In addition to these layers, the eyeball is divided into two chambers.
Vitreous Body
- Formed by a gelatinous structure.
- Located at the back of the eye.
Anterior Chamber
- Located at the front of the eye.
- Full of a colorless liquid.
The two chambers are separated by the crystalline lens.
Smell (Nostrils)
The nostrils are formed by:
Pituitary (Red or Respiratory) Membrane
- Located at the bottom of the nostrils.
- Designed to heat and clean the air we breathe.
Yellow Pituitary (Olfactory) Membrane
- Located on the top of the nostrils.
- Contains bipolar olfactory cells.
- These cells detect odors and connect to the olfactory bulb.
- The olfactory bulb is a membrane that collects and sends stimuli to the olfactory nerve.
Sense of Taste
Taste is due to receptors called taste buds.
- Taste buds are located in the pharynx, the palate, and especially on the tongue.
- Each taste bud is formed by two types of cells: taste cells, which are connected to nerve fibers, and supporting cells, which provide support.
- The sense of taste works in connection with the sense of smell to give us the taste of certain foods.
Sense of Touch
The skin has three layers:
Epidermis
- The outermost layer of the skin.
- Formed by stratified squamous epithelial cells.
- The innermost layer of the epidermis contains germ cells that give rise to the upper layers.
- The outermost cells are keratinized, meaning they are filled with a protein called keratin, which makes them tough and waterproof.
- This layer also contains melanin-producing cells, which produce the pigment that protects the skin from the sun.
- Sebaceous glands in the epidermis produce fatty substances that provide waterproofing.
Dermis
- Located beneath the epidermis.
- Formed by connective tissue, which is responsible for the strength and flexibility of the skin.
- Contains nerve endings, which can be free (for pain reception) or encapsulated (for sensations like pressure, cold, and heat).
- Also contains sweat glands, hair follicles, and blood vessels.
Subcutis (Hypodermis)
- The innermost layer of the skin.
- Formed by adipose tissue, which contains an abundance of fat cells.
- Functions to thermally insulate the body and provide shock absorption.
Nutrition
Nutrition is the process by which organisms acquire materials and energy to carry out vital functions. Human nutrition is heterotrophic, meaning we obtain nutrients from other organisms. Several systems are involved in nutrition:
Digestive System
- Responsible for breaking down food and absorbing nutrients.
Respiratory System
- Responsible for taking in oxygen and releasing carbon dioxide.
Circulatory System
- Carries nutrients and oxygen to the body’s cells and removes waste products.
Urinary System
- Removes toxic substances from cellular metabolism.
Digestive System
Structure
The digestive system consists of the digestive tract and attached glands.
Digestive Tract
Mouth
- The opening of the digestive tract that communicates with the outside.
- Contains the lips, teeth, tongue, and other structures.
Pharynx
- A duct that communicates with the mouth and nostrils at the top and the esophagus and larynx (voice box) at the bottom.
- Common to both the digestive and respiratory systems.
Esophagus
- A duct that connects the pharynx to the stomach.
Stomach
- A widened part of the digestive tract that consists of several regions:
- Fundus: The upper part of the stomach.
- Cardia: The part of the stomach where the esophagus connects.
- Body: The central part of the stomach.
- Pyloric Antrum: The lower part of the stomach that connects to the small intestine.
Small Intestine
- About 7 meters long and highly folded to increase surface area for absorption.
- Contains villi and microvilli, which further increase surface area.
- Consists of three parts:
- Duodenum: The first part of the small intestine.
- Jejunum: The middle part of the small intestine.
- Ileum: The last part of the small intestine, which connects to the large intestine.
Large Intestine (Colon)
- At the beginning of the large intestine is a sac-shaped area called the cecum, which has an extension called the appendix.
- The large intestine does not have villi.
Rectum and Anus
- The rectum is a tube about 15-20 cm long that ends in the anus, which is the opening of the digestive tract to the outside.