A Comprehensive Guide to Human Biology: Cells, Tissues, and Systems

Posted on Aug 24, 2024 in Biology

1. Tissues: Definition and Types

Tissues are collections of similar cell types surrounded by a similar extracellular matrix (ECM). The four major tissue types are:

  1. Muscle
  2. Nervous
  3. Epithelial
  4. Connective

2. Organs: Definition and Example

An organ is a collection of two or more primary tissues organized into a functional unit. For example, the stomach comprises:

  • Epithelial lining
  • Muscular layer (for mixing stomach contents)
  • Nervous tissue (for coordinating muscular action)
  • Connective tissue (for binding tissues into a functional unit)

3. Tissue Integrity

Tissues maintain their structure outside the body due to cell-cell and cell-matrix adhesion molecules. These molecules attach cells to each other and the ECM, providing mechanical and structural support.

4. Cell Culture

Cell culture is the maintenance and growth of cells outside of the body.

5. Cell Culture Media

Cell culture media is the liquid used to support cell growth in culture. It must be sterile, maintain a buffered pH of 7.4 with an indicator dye, be salt-balanced, and contain all necessary nutrients, vitamins, and growth factors.

6. Cell Isolation for Culture

Cells are isolated for culture by dissecting tissues into small pieces. This can be achieved through enzyme degradation (using enzymes to break down bonds) or explantation (placing tissue pieces in growth media).

7. Somatic Cell vs. Cell Line Life Cycles

Somatic cells undergo a repetitive life cycle of division (resting, interphase, mitosis), producing two diploid daughter cells. Their life cycle is shorter than that of germ cell lines. Meiosis, specific to germ cell division, involves two divisions (meiosis I and meiosis II) resulting in four haploid daughter cells.

8. Prokaryotic vs. Eukaryotic Cells

Five key differences between prokaryotic and eukaryotic cells are:

  1. Size: Prokaryotic cells are usually smaller.
  2. Cell Wall: Prokaryotes have a cell wall for shape maintenance, while eukaryotic cells have a cytoskeleton.
  3. DNA Storage: DNA is stored in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells.
  4. DNA Structure: Eukaryotic cells have tightly packed linear DNA, while prokaryotic cells have circular DNA in the cytoplasm.
  5. Organelles: Prokaryotic cells lack cytoplasmic organelles like lysosomes, ER, mitochondria, and the Golgi apparatus.

9. Endoplasmic Reticulum (ER)

The ER is an organelle in eukaryotic cells made up of interconnected membranous spaces. The rough ER, studded with ribosomes (sites of protein synthesis), is easily recognizable. The smooth ER, lacking ribosomes, synthesizes lipids and attaches receptors to cell membrane proteins.

10. Golgi Apparatus

The Golgi apparatus, an organelle in eukaryotic cells, is composed of stacks of membrane-bound structures called cisternae. It receives proteins from the rough ER in vesicles for secretion and integration with the membrane.

11. Lateral Diffusion in Plasma Membrane

Scientists can demonstrate lateral diffusion of proteins in the plasma membrane by fusing human and mouse cells. Freezing one sample and keeping the other warm, followed by adding a fluorescent antibody, reveals protein segregation in the frozen sample and mixing in the warm sample, indicating lateral diffusion.

12. Identifying Exoplasmic Proteins

Membrane proteins on the extracellular face are glycosylated. Scientists can identify them by the presence of large attached sugars.

13. Endomembrane System

The endomembrane system encompasses all membranes surrounding organelles within a cell’s cytoplasm. This includes the ER, Golgi apparatus, lysosomes, vacuoles, vesicles, and the cell membrane, but excludes mitochondria and chloroplasts.

14. Lysosomes

Lysosomes, part of the endomembrane system, are acidic organelles containing degradative enzymes for recycling worn cell components.

15. Cellular Pathways Utilizing Lysosomes

Three cellular pathways utilizing lysosomes are:

  1. Phagocytosis: Ingestion of dying cells or extracellular material (e.g., microbes) in a vesicle, which fuses with a lysosome for digestion.
  2. Endocytosis: Molecules taken up from the outside in endosomes, which fuse with lysosomes for digestion.
  3. Autophagy: Digestion of old or unneeded organelles or proteins.

16. Cytoskeleton Functions

The cytoskeleton has three major functions:

  1. Mediates changes in cell shape.
  2. Mediates cell motility.
  3. Mediates cell morphology.

17. Cytoskeleton Structure

The cytoskeleton, an internal skeleton providing cell shape and coordinating cell division and movement, comprises three types of protein filaments forming interconnected networks:

  1. Microfilaments
  2. Intermediate filaments
  3. Microtubules

18. Extracellular Matrix (ECM)

The ECM, found in the extracellular space of all tissues, is composed of:

  1. Fibrillar proteins: Collagens and elastins
  2. Multiadhesive proteins: Fibronectin and laminin
  3. Hydrophilic proteoglycans: Bind water and growth factors

19. Types of ECM

The two major ECM types are the basal lamina (underlying epithelial tissues) and stromal ECM (all other ECM).

20. Basal Lamina

The basal lamina, a sheet-like ECM supporting epithelial tissues, is composed of:

  1. Type IV collagen: Provides strength
  2. Laminin: Links epithelial cell basement membranes to collagen fibers
  3. Hydrophilic proteoglycans: Bind water and provide cushioning

21. Connective Tissue Diversity

Cartilage, made of type II collagen and rich in proteoglycans, resists compression due to high water content. Tendons, rich in type I collagen, connect muscle to bone and provide tensile strength.

22. Immortalized Cell Lines

Immortalized cell lines are cells that have undergone oncogenic transformation, allowing indefinite division (like cancer cells). These cells are commercially available for in vitro studies.

23. Human Body’s Communication Systems

The three major communication systems in the human body are:

  1. Nervous system: Signals via neurotransmitters
  2. Endocrine system: Signals via hormones
  3. Immune system: Signals via cytokines

24. Steps in Extracellular Signaling

Six common steps in extracellular signaling systems are:

  1. Synthesis of a signaling molecule
  2. Release of the signaling molecule by a signaling cell
  3. Transport of the signal to the target cell (convection and diffusion)
  4. Binding of the signaling molecule to a specific receptor protein
  5. Change in cellular metabolism or function due to signal binding
  6. Removal/termination of the signal

25. Signaling Molecule Distances: Nervous System

The nervous system uses neurotransmitters, synthesized at presynaptic terminals and released into the synaptic cleft (20-40nm wide). They diffuse across this gap to bind and activate receptors on the post-synaptic cell.

26. Signaling Molecule Distances: Endocrine System

The endocrine system uses hormones secreted into the bloodstream. These hormones diffuse throughout the bloodstream until they reach their target cells, where they bind to receptors.

27. Ligand-Receptor Interaction

A ligand is a molecule that binds to a specific site on a protein (the receptor). This binding alters the receptor’s conformation, initiating signal transmission into the cell.

28. Types of Cellular Receptors

Two types of cellular receptors are:

  1. Cell surface receptors: Located on the cell surface, they typically trigger second messengers.
  2. Intracellular receptors: Binding occurs inside the cell, often leading to longer-term effects involving protein synthesis. Ligands are often intracellular second messengers from previous bindings.

29. Pancreas and Diabetes

The pancreas regulates glucose metabolism through insulin and glucagon, hormones with reciprocal interactions on the liver, fat tissue, and somatic tissues.

30. Islets of Langerhans

The islets of Langerhans are discrete cell collections in the pancreas that secrete hormones. An adult human pancreas contains about 1 million islets, composed of alpha (glucagon) and beta (insulin) cells.

31. Immune System

The immune system, comprising organs, glands, cells, and molecules, protects against disease and aids wound healing. It has two branches: innate and adaptive immunity.

32. Complement System

The complement system is a self-amplifying enzymatic cascade that attacks foreign cell surfaces. It involves about 30 glycoproteins in blood plasma, cell surface receptors, and antibodies from B-cells, activating inflammation, phagocytosis, and cell lysis.

33. Components of the Innate Immune System

The major components of the innate immune system are:

  1. Antibodies
  2. Complement and phagocytic cells (white blood cells and tissue macrophages)

34. Functions of the Innate Immune System

The four major functions of the innate immune system are:

  1. Aggregation: Clumping of antigen-bearing agents
  2. Opsonization: Tagging microbes for phagocytosis
  3. Chemotaxis: Attracting neutrophils and macrophages
  4. Lysis: Rupturing microbial cells

35. Metabolism and Oxygen

Metabolism refers to all chemical reactions that break down nutrients for energy and monomers for biopolymer synthesis. Oxygen is essential for energy extraction, coupled with ATP synthesis, as it’s required for dismantling nutrients into CO2 and H2O.

36. Cellular Respiration

Cellular respiration, occurring in all cells, converts biochemical energy from nutrients to ATP. It involves glucose uptake and takes place partly in the cytoplasm (glycolysis) and partly in the mitochondria (TCA cycle). Inputs are glucose and oxygen, while outputs are ATP, CO2, and H2O.

37. ATP: The Power Currency of the Cell

ATP is used by living cells for:

  1. Synthesis of cellular macromolecules
  2. Powering cellular movements
  3. Transporting molecules against concentration gradients
  4. Producing heat

38. Respiratory Airways

The respiratory airways consist of the conducting portion (nasal cavities, pharynx, larynx, trachea, bronchi, bronchioles) with no gas exchange and the respiratory portion (respiratory bronchioles leading to alveoli) where gas exchange occurs.

39. Components of the Gastrointestinal Tract

The major components of the human gastrointestinal tract are:

  1. Mouth
  2. Pharynx
  3. Esophagus
  4. Stomach
  5. Duodenum
  6. Jejunum
  7. Small intestine

40. Glandular Organs of the Digestive System

The four major glandular organs associated with the human digestive system are:

  1. Salivary glands
  2. Liver
  3. Gall bladder
  4. Pancreas

41. Activities of the Digestive System

The four major activities of the human digestive system are:

  1. Motility: Movements that mix and propel contents along the GI tract
  2. Secretion: Glands releasing water and substances into the GI tract
  3. Digestion: Hydrolysis of ingested biopolymers into monomers
  4. Absorption: Nutrient monomers entering the bloodstream from the GI tract

42. Layers of the GI Tract

The GI tract has four layers:

  1. Mucosa: Epithelial layer
  2. Submucosa: Contains blood vessels
  3. Muscularis propria: Inner circular and outer longitudinal muscle fibers
  4. Serosa: Outer connective tissue layer