Cell Biology, Nutrition, Circulation and Excretion Explained

Cell Structure and Organelles

Cell: the smallest functional unit that performs the three vital functions: nutrition, relation and reproduction.

Cell membrane: a thin limit around the cell. Its function is to regulate the passage of substances.

Cytoplasm: contains many organelles. Its function is to host cellular processes.

• Mitochondria: cellular respiration.
• Cytoskeleton: supports the cell and drives mitosis.
• Ribosomes: synthesize proteins.
• Endoplasmic reticulum: transports substances.
• Golgi apparatus: packages and sends out proteins and glucids.
• Vacuoles: store and eliminate substances.

Nucleus: contains DNA, which protects the cell and carries genetic information.

The Cell and Its Vital Functions

Cell: a functional unit that develops the three vital functions: nutrition, relation and reproduction.

Nutrition: the cells of heterotrophs obtain nutrients from their environment, which they then digest.

Relation: cells can react to external stimuli, such as those that are received and processed by the nervous system.

Reproduction: cells reproduce through mitosis.

Types of Tissues

• Epithelial tissue: cells are densely packed, with little intercellular matrix; it protects and covers surfaces.
• Connective tissue: contains fibroblasts and a rich extracellular matrix with fibers.
• Adipose tissue: made of adipocytes that store fat in a matrix.
• Cartilage: made of chondrocytes in a hard extracellular matrix.
• Bone: osteocytes in a mineralized and rich matrix of minerals.
• Blood: formed by erythrocytes, leukocytes and platelets in a liquid matrix.
• Muscle tissue: skeletal muscle fibers, smooth and cardiac muscle cells.
• Nervous tissue: neurons, which transmit impulses along nerves.

Organs: structures formed by different tissues that work together to perform a specific function.

Apparatus and systems: sets of organs that work together to perform a common function.

Nutrition and Nutrients

Nutrients: substances that provide energy and materials needed to maintain life and growth.

Food: products that contain nutrients.

• Carbohydrates (glucids): function to provide energy.
• Lipids: function to provide energy and store triglycerides in animal tissues. Cholesterol is also a lipid.
• Proteins: have structural functions, form enzymes, make up antibodies, and are part of cell membranes and some hormones such as insulin.
• Water: makes up most of the body and transports nutrients.
• Mineral salts: form structural components such as bones and teeth, and maintain body balance.

Diet: the type of food normally consumed, which should be in the right proportion.

The Digestive System

Nutrition: the process by which the body absorbs and assimilates nutrients, and obtains energy.

Digestive tract: consists of organs that transform food into nutrients and transport them through the digestive tube and glands.

• Oral cavity: food is received and broken down by the teeth. The tongue and teeth are part of the oral cavity, along with three pairs of salivary glands.
• Pharynx: connects the oral cavity with the esophagus.
• Esophagus: connects the pharynx with the stomach.
• Stomach: entry of food, exit through the pylorus. Gastric juice breaks down proteins and forms chyme.
• Small intestine: divided into three sections: duodenum, jejunum and ileum. Digestion is completed here with intestinal juice, bile and pancreatic juice.
• Large intestine: divided into three parts: cecum, colon and rectum.
• Salivary glands: three pairs that produce saliva.
• Liver: located under the diaphragm on the right side. It produces bile, which emulsifies fats, and stores glucose.
• Pancreas: a gland that secretes pancreatic juice into the duodenum, containing digestive enzymes.

Circulatory system: responsible for distributing nutrients throughout the body and collecting waste products from cells. Formed by blood, heart and blood vessels.

Blood: a connective tissue with a liquid plasma matrix and cells: red blood cells, white blood cells and platelets.

Plasma: made of water and dissolved substances such as nutrients.

Red blood cells: responsible for transporting oxygen.

White blood cells: responsible for producing antibodies and phagocytosing microbes.

Platelets: involved in blood clotting.

Heart: a muscle that contracts (systole) and relaxes (diastole) rhythmically, pumping blood to the whole body. It has four cavities: right atrium, right ventricle, left atrium and left ventricle.

Lymphatic system: responsible for returning plasma from intercellular spaces to the blood. Formed by lymph, lymphatic capillaries, lymphatic vessels and lymph nodes.

Lymph: a fluid circulating inside the lymphatic vessels.

Lymphatic capillaries: thin vessels that reabsorb interstitial plasma.

Lymphatic vessels: formed by the confluence of capillaries.

Lymph nodes: enlargements of lymphatic vessels where lymphocytes are formed.

Cellular Respiration and Pulmonary Respiration

Cellular respiration: the process by which oxygen is captured in the lungs and used by cells to break down digested food and obtain energy. It takes place inside the mitochondria.

Pulmonary respiration: captures oxygen from the air and eliminates carbon dioxide, which is carried by the blood. It takes place in the lungs.

• Nasal cavities: two cavities separated by the nasal septum that form part of the respiratory apparatus.
• Pharynx: the tonsils help produce antibodies.
• Larynx: a small duct that contains the vocal cords.
• Trachea: a duct formed by flexible cartilage that facilitates the passage of air.
• Bronchi: two ducts that branch into bronchioles.
• Lungs: made of millions of bronchioles that end in alveoli, where gas exchange occurs.
• Respiratory muscles: intercostal muscles and the diaphragm. When the intercostal muscles contract, the ribs rise, and when the diaphragm contracts, it moves down.

Excretion

Excretion: the elimination of harmful or useless substances produced by the body.

• Excretory organs: the urinary system eliminates toxic nitrogenous compounds dissolved in blood.
• Lungs: eliminate carbon dioxide produced by cellular respiration.
• Skin: eliminates water, mineral salts and urea through sweat.
• Kidney: a renal layer made of a set of structures surrounded by the renal capsule.
• Cortical zone: made of renal corpuscles.
• Medullary zone: formed by tubules connected to nephrons and collecting ducts. The tubules are grouped in renal pyramids.
• Renal pelvis: a zone in the kidney where collecting ducts converge into the ureter.
• Ureters: carry urine from the kidney to the bladder.
• Bladder: a sac where urine is temporarily stored before excretion.
• Urethra: expels urine to the exterior (urination).