Cellular anatomyTissues types

Levels of organization… Cells Tissues Tissues Organs

Cellular Anatomy Cell organelles

Cellular Anatomy Selected human cell structures

Nucleus: DNA’s home

Cellular Anatomy Selected human cell structures

Ribosomes, endoplasmicreticulum & Golgi apparatus:protein builders

Cellular Anatomy Selected human cell structures

Lysosomes: digesters

Cellular Anatomy Selected human cell structures

Mitochondria:ATP factories

Cellular Anatomy Selected human cell structures

Plasma membrane Selectively-permeable Membrane proteins

Membrane Transport Diffusion Filtration Facilitated diffusion Active transport Endocytosis Exocytosis

Tissue Types Epithelium: Covering/lining

Secretion, absorption, filtration, diffusion

Tissue Types Connective tissue: Connects/supports

Tissue Types Muscular tissue: Contracts to cause movement

Tissue Types Nervous tissue: Sends electrochemical messages

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Cellular anatomyTissues types

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Levels of organization… Cells Tissues Tissues Organs

We’ll be spending the next several days looking at tissues. As a reminder, a tissue is a collection of cells doing the same job together. Two or more different types of tissues working together make up an organ. This picture shows a cross-section of skin (an organ). The superficial layers (stained purple) are epithelium. Notice that the epithelium consists of many cells clustered close-together. The deeper pink-staining region is connective tissue. There are fewer cells in connective tissue.

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Cellular Anatomy Cell organelles

Think back to your biology class. You may remember that cells are the basic units of life. That means that cells are small units that demonstrate all of life’s processes, and that all living things are made up of cells. Each cell has many structures, called organelles, inside of it that carry out the cell’s life processes.

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Cellular Anatomy Selected human cell structures

Nucleus: DNA’s home

At some point in their lives, all cells have at least one nucleus. Most mature cells have exactly one nucleus, though there are expections. Mature red blood cells have no nucleus, for example, while skeletal muscle cells have many nuclei. The nucleus houses the cell’s DNA, which has the instructions for what molecules the cell can make. The DNA in each cell is identical, but different cells might have different parts of the DNA “turned on.” This is why the nucleus, with its DNA, can be considered the “director” of a cell’s activity.

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Cellular Anatomy Selected human cell structures

Ribosomes, endoplasmicreticulum & Golgi apparatus:protein builders

I’ve included these three structures together because they’re all involved in the same process: manufacturing molecules and preparing them for secretion. Ribosomes manufacture proteins while endoplasmic reticulum manufactures lipid-based molecules. The ER is also involved in moving newly-made substances to the Golgi apparatus, which then packages the substances into vesicles. Many vesicles are secretory vesicles, which remain in the cell until the cell is ready to secrete the molecules. Then, the vesicles fuse with the plasma membrane and release their contents outside the cell.Cells that do a lot of secretion (e.g. glandular cells) will have large amounts of ER and Golgi apparatus.

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Cellular Anatomy Selected human cell structures

Lysosomes: digesters

Lysosomes are large vesicles (made by the Golgi apparatus) filled with digestive enzymes. Their job is to fuse with other things inside the cell – food vacuoles, worn-out cell parts, or engulfed bacteria – and digest them, effectively using those particles as food for the cell. Lysosomes also play a role in cell suicide. If they release their digestive enzymes near the plasma membrane, the cell may burst and die.Cells involved in absorption and digestion, such as macrophages which engulf invading bacteria, have many lysosomes.

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Cellular Anatomy Selected human cell structures

Mitochondria:ATP factories

Mitochondria are the “powerhouses” of a cell. They carry out aerobic respiration which uses oxygen to “burn” simple sugars and make large amounts of ATP. ATP is a useable form of chemical energy which is used to power the chemical reactions inside cells. Cells can produce a small amount of ATP anaerobically (without oxygen) in the cytoplasm, but this doesn’t yield nearly enough ATP to run all of the chemical reactions to support life in human cells.Cells that require a lot of ATP, such as muscle cells, will have huge numbers of mitochondria.

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Cellular Anatomy Selected human cell structures

Plasma membrane Selectively-permeable Membrane proteins

The plasma membrane is the “skin” of a cell. It separates the cell’s cytoplasm and intracellular fluid from the interstitial fluid on the outside. It is made of two layers of phospholipids – molecules that have a polar end and a nonpolar end. The plasma membrane is selectively-permeable, which means that some substances can move across it freely while others cannot. Generally, nonpolar molecules and very small substances can diffuse across the membrane while large or polar molecules cannot.There are many different types of membrane proteins embedded in the plasma membrane. These proteins carry out many functions, such as identifying the cell, activating enzymes inside the cell, responding to chemical signals, and transport. The transport proteins are involved in moving substances into and out of the cell that cannot otherwise cross the selectively-permeable membrane.

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Membrane Transport Diffusion Filtration Facilitated diffusion Active transport Endocytosis Exocytosis

The most important cell process to our class is membrane transport – moving substances across the plasma membrane between the cytoplasm and the interstitial fluid. There are several ways this happens.•Diffusion: Diffusion is one of the most fundamental laws of physics. Substances will always tend to spread out from an area where they are highly-concentrated to an area where they are less-concentrated. For molecules that can cross the plasma membrane, diffusion can also happen across the membrane. For example, oxygen gas is a nonpolar molecule and can easily move across the cell membrane. If there is a high concentration of oxygen outside a cell, and less inside the cell, the oxygen can just passively diffuse into the cell. Carbon dioxide is another gas that is nonpolar and can diffuse across the membrane. Diffusion does not require any energy. It just happens.•Filtration is another type of movement directly across the plasma membrane. It is different from diffusion, though, because pressure can cause molecules to move against their concentration gradient. In other words, molecules such as water can be forced to move from an area where there is little water to an area where there is already a lot. Filtration occurs in the kidneys.•Facilitated diffusion is just like simple diffusion above, except that it can happen with molecules that cannot cross the plasma membrane. For this to happen, there has to be an open transport protein in the membrane that allows the molecule to pass. Think of these transport proteins like tunnels through a mountain or doors in a wall. As long as the tunnel or door is open, diffusion can happen through them, even though the molecules can’t go straight across the membrane otherwise.•Active transport is the opposite of diffusion in almost every way. Active transport actively pumps molecules across the plasma membrane, often against the concentration gradient. This requires ATP energy to power the pumps. In fact, most of the ATP used by some cells goes to powering active transport pumps.•Endocytosis is a way of bringing large particles (food or bacteria, for example) into a cell. The cell bends its plasma membrane around the particle, complely engulfing it and forming a vesicle around it. The particle is then “dragged” into the cell to be digested by lysosomes or stored.•Exocytosis is how secretion occurs. A secretory vesicle (made by the Golgi apparatus, remember?) moves to the plasma membrane, fuses with it, and dumps its contents outside of the cell, into the interstitial fluid or blood.

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Tissue Types Epithelium: Covering/lining

Secretion, absorption, filtration, diffusion

Recall that there are four types of tissues. Epithelial tissue (or epithelium) is a tissue that covers or lines all of the body’s internal and external surfaces. The epidermis of the skin is epithelium. Mucous membranes line all of the body’s cavities that open to the outside world (oral cavity, nasal cavity, stomach, rectum, etc.). Serous membranes line the body’s internal cavities.Which each epithelial tissue generally carries out just one job, there are several jobs that epithelium is well-suited for. Some epithelial tissues, called glands, secrete chemicals onto surfaces, into cavities, or into the blood. Some absorb and digest nutrients. Others pass materials from blood to underlying tissues through diffusion or filtration.

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Tissue Types Connective tissue: Connects/supports

Connective tissue joins various tissue types together and provides support and protection to many other tissues. Examples of connective tissue include the bones, cartilages, blood, and fat cells. Compared to epithelium, connective tissue has far fewer cells and much more non-living extracellular matrix.

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Tissue Types Muscular tissue: Contracts to cause movement

Muscular tissue is unique because it can shorten to cause movement. This includes both skeletal movement (movement of the bones and facial features) as well as visceral movement (movement of substances through the body).

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Tissue Types Nervous tissue: Sends electrochemical messages

Nervous tissue is responsible for fast communication throughout the body. By sending electrochemical impulses between the body’s periphery and the central nervous system (the brain and spinal cord), we are able to be aware of our environment and respond to changes in the environment.

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