Human Body: Functions, Systems, and Anatomy

Posted on Dec 12, 2024 in Biology

Living Things vs. Non-Living Things

Living things possess life and include animals, bacteria, and algae. They move, reproduce, and nurture relationships. These are the three vital functions.

  • Heterotrophic Animal Nutrition
  • Autotrophic Plant Nutrition: Photosynthesis
  • Fungi: Heterotrophic nutrition (they are not plants because they acquire food by absorption, not ingestion)

All plants adapted to the air environment (not water) have a root, stem, and leaf. However, moss does not, as it represents an evolutionary step from water to land. For example, algae are photosynthetic but cannot live in an air environment because their structure is too weak.

Non-living things include minerals like coal and salt, rocks like slate, and molecules. Living beings store genetic information.

  • Bacteria are single-celled creatures.
  • Fungi include yeast (unicellular), molds (multicellular), and mushrooms.

Fungi are not plants because their nutrition is heterotrophic. Protozoa are a group of organisms that live in water, inside the human body, and in animals. They move very easily.

Fungi always live on organic matter, have heterotrophic nutrition, and are multicellular.

Nutrition: Functions of the Human Body

Human Nutrition:

Glucose + O2 → CO2 + H2O + Energy

Glucose produces water, but not all foods contain glucose. Glucose is needed for energy.

How are Digestion, Circulation, Respiration, and Excretion Related?

  1. Food enters through the mouth.
  2. Food goes to the digestive system.
  3. The circulatory system transports glucose.
  4. Oxygen is breathed in through the respiratory system.
  5. The circulatory system transports oxygen.
  6. Air is expelled through the lungs (excretion).

The Digestive System

The digestive tract includes:

  1. The oral cavity, pharynx, and esophagus
  2. The stomach (gastric digestion)
  3. The liver and pancreas
  4. The intestines (intestinal digestion and absorption)

Digestion transforms food into smaller materials. Chemical digestion involves enzymes (proteins) secreted by glands that communicate with the digestive tract. These enzymes break down polymers (like polysaccharides) into monomers (like glucose).

Salivary glands digest carbohydrates, while gastric glands, the intestine, pancreas, and liver digest everything. Digestion occurs in the first part of the digestive tract (from the mouth to the duodenum). Food moves through the digestive tract via peristaltic movements.

The Oral Cavity

a. Tongue: A muscular organ with taste buds (sweet, salty, sour, and bitter). The papillae contain dissolved substances that stimulate the sense of taste.

b. Teeth: Hard pieces that cut, tear, and grind food, making it easier for enzymes to break down. Teeth are composed of enamel (calcium phosphate), dentin (similar to ivory), pulp (living tissue with nerves and blood vessels), and cement (lining the root).

c. Pharynx: The crossing of the pharynx and respiratory tract includes the buccal cavity, esophagus (digestive), larynx (respiratory), and Eustachian tubes (leading to the middle ear). The epiglottis regulates the entry to the larynx.

The Esophagus

A tube about 25 cm long located between the trachea and the spine. It passes through the diaphragm and connects to the digestive tract.

The Stomach

An expansion below the diaphragm with a capacity of about 2.5 liters. The inner part is covered by a gastric mucosa that secretes gastric juice. The food bolus becomes chyme due to the action of gastric juice.

The Liver and Pancreas

a. Liver: Weighing 1.5 kg, the liver has multiple functions, including digestion, defense, storage, and manufacturing.

b. Pancreas: An organ located behind the stomach, about 15 cm long and weighing 80 grams. It secretes pancreatic juice (containing enzymes to digest all kinds of small biomolecules) and insulin (allowing glucose to pass from the blood into cells).

The Intestines

Between 8 to 9 meters long, the intestines are surrounded by a protective membrane called the peritoneum. Blood vessels collect and move nutrients through the mesenteric veins to the portal vein, ending in the liver.

The intestinal villi are responsible for absorption. The small intestine is differentiated from the large intestine, which is 2 to 3 meters long. Most of the water and salts released during digestion are absorbed in the large intestine. The chyme, now called the kilogram, consolidates and hardens.

The large intestine, particularly the transverse colon, contains a large amount of bacteria that perform various functions, including absorption of salts and water, chemical transformation of trace gases, synthesis of vitamin K (needed for blood clotting), and defense against harmful bacteria.

Circulation

  1. The circulatory system and blood
  2. The heart
  3. Blood vessels
  4. Blood circulation
  5. The lymphatic system

The Circulatory System

The circulatory system has three main functions:

  • Distribute nutrients and oxygen throughout the body
  • Collect waste products (CO2, uric acid, etc.)
  • Transport defenses (white blood cells and antibodies) and hormones

It consists of:

  • Blood: Fluid containing blood cells
  • Heart: Muscular pump that drives the blood
  • Blood and lymphatic vessels: Conduits through which blood circulates

Blood

Blood is a slightly salty tissue formed by a viscous yellowish liquid called plasma and cellular elements. A person’s blood volume is approximately 7% of their body weight.

Plasma contains:

  • Nutrients (glucose, amino acids) and saltwater
  • Waste products (from the liver to the kidneys)
  • CO2 going to the lungs
  • Hormones secreted by glands to target cells
  • Other substances like fibrinogen (clotting), antibodies (defense), and heparin (anticoagulant)

Blood Cells

Red blood cells (erythrocytes) lose their nucleus after formation to contain the maximum possible hemoglobin. Hemoglobin binds to oxygen (Hb-O2, red) and transports it through the iron it contains. There are between 4-5 million red blood cells per mm3. Iron, red blood cell, or hemoglobin deficiency is called anemia.

White blood cells (leukocytes) have nuclei of various shapes. They can exit blood vessels (diapedesis). Some white blood cells digest bacteria and dead cells, while others produce antibodies that destroy bacteria or other pathogens.

Platelets (thrombocytes) are cell fragments that contain substances necessary for blood clotting.

The Heart

Structure:

  • Vena cava: Receives blood from the body
  • Pulmonary veins: Receive blood from the lungs
  • Right atrium: Receives blood from the vena cava
  • Right ventricle: Sends blood to the lungs through the pulmonary arteries
  • Left atrium: Receives blood from the pulmonary veins
  • Left ventricle: Sends blood to the body through the aorta
  • Coronary artery: Supplies blood to the heart muscle

The heart has a conical shape with the tip directed downwards and inclined to the left. It is located on the diaphragm, between the two lungs.

Function:

  • Systole: Compression phase (ventricular contraction)
  • Diastole: Relaxation phase

Right side: Receives deoxygenated blood from the body through the vena cava and sends it to the lungs through the pulmonary arteries.

Left side: Receives oxygenated blood from the lungs through the pulmonary veins and sends it to the body through the aorta.

The heart has an independent electrical system with two nodes that produce electrical impulses rhythmically (depending on the oxygen concentration in the blood):

  • Sinoatrial node (pacemaker): Located in the right atrium, initiates atrial systole (top to bottom)
  • Atrioventricular node: Initiates ventricular systole (bottom to top)

Blood Vessels

The contraction of the ventricles pumps blood into the arteries, which branch into smaller arterioles and then into capillaries. Capillaries are so small that red blood cells skim their walls, allowing for the exchange of gases and substances. Capillaries then merge into venules and finally into veins.

Arteries: Vessels that leave the heart and distribute blood throughout the body. They have elastic walls and can widen (during blood flow or hypertension) or narrow (during low blood flow or hypotension).

Veins: Vessels that return blood to the heart.

Circulation:

  1. Pulmonary (minor) circulation: Oxygenates the blood
  2. Systemic (major) circulation: Sends oxygenated blood to all organs for cellular respiration

The Lymphatic System

Collects waste substances and nutrients from intercellular spaces. Movement is facilitated by muscle contractions.

The Respiratory System

Captures oxygen from the air and delivers it to the circulatory system, while expelling carbon dioxide.

Upper respiratory tract: Includes the nasal cavity, pharynx, and larynx. The bronchial mucosa is covered and has other functions.

Lower respiratory tract: Located in the respiratory cavity, it is highly internal, branched, and irrigated by capillaries to maximize the surface area for gas exchange.

Nasal cavity: The turbinates slow down the airflow, allowing the pituitary gland (superficial blood vessels) to heat and humidify the air. The olfactory epithelium detects smells. The sinuses are cavities that can fill with mucus, trapping particles, bacteria, and viruses.

Pharynx: Connects the nasal cavity, mouth, esophagus, and larynx. It contains tonsils with white blood cells.

Larynx: Protected by cartilaginous structures like the hyoid bone and thyroid cartilage (with a prominent”Adam’s appl” in males). The thyroid gland, important for nutrient metabolism, is located nearby.

Vocal cords: The most significant feature of the larynx.

Trachea: An endoscope of the trachea reveals cilia and mucous cells as a last defense before the bronchi and lungs. It divides into two bronchial ducts at the end.

Lungs: Two spongy organs (the left with 2 lobes and the right with 3) covered by a protective membrane (pleura) to facilitate sliding within the thoracic cavity. The thoracic cavity is bounded by the ribs, intercostal muscles, and diaphragm (a muscle that separates the respiratory and gastrointestinal cavities). The lungs contain air sacs or pulmonary saccules that end in expansions shaped like clusters (500 million small sacs called alveoli with very thin walls) surrounded by capillaries. This facilitates gas exchange and minimizes water loss.

Pulmonary ventilation: The process of air renewal that fills the lungs.

Muscles involved:

  • Intercostal muscles (widen the cavity)
  • Ribs
  • Diaphragm (lowers the cavity)
  • Pleura (membranes that keep the lungs attached to the ribs)

A pneumothorax occurs when the pleura is pierced, separating the lung from the ribs and causing air to escape.

Two stages of ventilation:

  1. Inspiration: Active phase with increased cavity volume and decreased internal pressure (air enters)
  2. Expiration: Relaxation phase with increased internal pressure, causing air to exit

Air volumes:

  • Inspired air: Oxygen-rich, tidal volume 0.5 liters
  • Expired air: Oxygen-poor, CO2-rich, tidal volume 0.5 liters
  • Inspiratory reserve volume (forced): 3 liters
  • Expiratory reserve volume (forced): 1 liter
  • Residual volume: 1.5 liters
  • Total lung capacity: 0.5 + 3 + 1 + 1.5 = 6 liters

Gas exchange:

At the alveolar level:

  1. Oxygen, in high concentration, is recruited and binds to hemoglobin (it is later released near cells with high oxygen consumption).
  2. CO2, in high concentration in the blood reaching the alveoli, is released.

Excretion

The expulsion of useless or harmful products from cells (cellular excretion) and blood (bodily excretion).

Excreted substances:

  1. CO2 and H2O produced during mitochondrial respiration
  2. Ammonia (NH3, transformed into urea) from protein metabolism
  3. Excess mineral salts dissolved in the blood
  4. Other substances like drugs and additives accumulated in the blood

The Urinary Tract

Composed of:

  1. Kidneys: Located near the back, surrounded by protective fat, and bean-shaped
  2. Ureters: Tubes that carry urine, about 25 cm long
  3. Urinary bladder: A sac that stores urine until expulsion, with a capacity of 300-1500 cm3
  4. Urethra: The tube that expels urine (urination). In males, it is also part of the reproductive system.

Renal Anatomy

  1. Renal capsule: Provides consistency to the kidney
  2. Cortical area: Contains renal corpuscles
  3. Medullary zone: Contains convoluted tubules and collecting ducts
  4. Renal pelvis: Collects urine from the collecting ducts

Locomotion

Locomotion is the ability of living things to move from one place to another. This requires the locomotor system, which includes:

a) Skeletal system

b) Muscular system

The Skeletal System

Consists of:

  • Bones: 206 rigid pieces in humans
  • Cartilage: Semi-rigid and flexible tissue
  • Joints: Unions between two or more bones
  • Ligaments: Connective tissue that joins bones or cartilage
  • Tendons: Connective tissue that joins muscles to bones and muscles to each other

Functions of the skeleton:

  1. Maintain body posture: Bipedalism
  2. Protect vital organs: Brain, spinal cord, lungs, and heart
  3. Provide attachment points for muscles: Facilitating movement
  4. Hematopoiesis: Generation of blood cells

Internal Bone Structure

Bones are not dead structures. They are formed by various tissues.

Bone tissue:

  • Diaphysis: The shaft of the bone
  • Epiphysis: The ends of the bone
  • Metaphysis: The growth plate, containing cartilage (ossifies over time)

Growth hormone (GH), sex hormones, and thyroid hormones influence bone growth.

Cartilage: Found in joints to facilitate movement and in growth areas.

Muscles

Muscles line the skeleton and give the body shape. They make movement possible. Muscle tissue has the unique ability to contract. Muscles are formed by elongated cells called muscle fibers.

The Nervous System

Responsible for:

  • Perceiving
  • Interpreting
  • Responding to external and internal stimuli

Consists of three systems:

  • Central Nervous System (CNS):
    • Brain
    • Spinal cord
  • Peripheral Nervous System (PNS):
    • Sensory nerves (input)
    • Motor nerves (output)
  • Autonomic Nervous System (ANS):
    • Sympathetic system
    • Parasympathetic system

Neurons

Cells of the nervous system specialized in receiving and responding to stimuli and producing nerve impulses. They require a continuous supply of glucose and oxygen.

Structure:

  1. Cell body (soma): Contains the nucleus and cytoplasm
  2. Dendrites: Short cytoplasmic extensions that receive signals
  3. Axon: Long extension of the cytoplasm that sends signals or responses

The Eye

A series of structures (iris, lens) focuses light onto the retina, which contains photoreceptors that are excited and transmit information to the optic nerve. Objects are projected as points and inverted. The brain completes and inverts the image. The two eyes allow for distance calculation. The movement of the ciliary muscles allows us to change the focus of the lens (myopia is difficulty seeing distant objects).

The Tongue

The tongue has 10,000 taste buds with chemoreceptors. A bitter taste can trigger a vomiting reflex.

The Brain

The brain is protected inside the skull and controls almost all body functions. The area responsible for the senses is relatively small in animals.

  • Cerebrum: Responsible for memory, intelligence, and consciousness. Divided into left and right hemispheres (receive information from the body and the exterior).
  • Cerebellum: Regulates motor activity.
  • Medulla oblongata: Controls automatic functions like breathing and heartbeats. It extends into the spinal cord.

The Spinal Cord

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