Animal Form Animal Form and and

FunctionFunction

Chapter 40 Chapter 40

Fate of Embryonic Cell Layers

What is a Tissue?

• The human body is composed of trillions of cells • There are approximately 200 cell types that

make up the trillions of cells• These 200 cell types can be further grouped into

4 categories according to their roles – these 4 categories are called tissues

• Tissues are groups of cells that function together to keep a body alive

• These cells are held together by a sticky extracellular matrix that either coats them or weaves them together.

Types of Tissues

• Epithelial Tissue (endoderm and ectoderm derived)

• Connective Tissue (mesoderm derived)

• Muscle Tissue (mesoderm derived)

• Neural Tissue (ectoderm derived)

Epithelial Tissue

Consist of 2 sub-categories:1. Epithelium2. Glandular

Epithelia are layers of epithelial cells that cover the internal or external surfaces of various organs, ducts, vessels, etc.

Glands are structures whose cells produce fluid secretions. They are either attached to epithelia or made from epithelia

Specialized Epithelial Tissue

• Endothelium (the inner lining of blood vessels, the heart, and lymphatic vessels) is a specialized form of epithelium.

• Another type, Mesothelium, forms the walls of the – pericardium (cavity that holds the heart), – pleurae (cavity that holds the lungs), and – peritoneum (cavity that holds the organs below the

diaphragm).

Characteristics of EpitheliaCharacteristics of Epithelia

• CellularityCellularity – made up entirely of cells that are closely – made up entirely of cells that are closely bound by tight junctions, gap junctions and desmosomesbound by tight junctions, gap junctions and desmosomes

• PolarityPolarity – One end of the tissue usually faces an – One end of the tissue usually faces an internal or external area of an organ internal or external area of an organ (apical surface)(apical surface) and and the other end is either attached to other tissues or a the other end is either attached to other tissues or a basement membrane called a basal lamina basement membrane called a basal lamina (basolateral (basolateral surface)surface)

• AvascularityAvascularity – Epithelia – Epithelia do not contain blood vesselsdo not contain blood vessels – they get their oxygen and nutrients from adjacent cells.– they get their oxygen and nutrients from adjacent cells.

• RegenerationRegeneration – Epithelial cells are constantly lost on – Epithelial cells are constantly lost on the exposed surface – so they are constantly replaced the exposed surface – so they are constantly replaced by cell division of stem cellsby cell division of stem cells

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What are the Functions of Epithelial Tissue?

• Provide Physical Protection – against abrasion, dehydration and destruction from chemical or biological agents

• Control Permeability – some allow substances to enter / leave or pass through, other epithelial cells are quite impermeable

• Provide Sensation – large sensory nerve supply

• Produce Specialized Secretions – These epithelial cells are called gland cells (Cells of the thyroid, salivary glands, etc.) They use blood and interstitial fluid as carriers of the chemicals they release

Even more about epitheliaI. Epithelial cells attach each other with tight

junctions, gap junctions and desmosomes

II. Attachment to the Basal Lamina

Epidermal cells hold each other as well as the basal lamina or basement membrane

Yet more about epithelia

III. Epithelial Maintenance and Repair

Stem cells or germinative cells within the epithelial tissue divide continually, to give rise to new epithelial cells to replace those that have died out due to exposure to toxic chemicals, pathogenic bacteria, abrasions, etc.

Types of Epithelial Tissue

(Epithelia)

Simple Squamous

• Thin, single layer of flat cells attached to basal membrane (lamina)

• Substances pass through very easily• Forms walls of capillaries, lines other

blood and lymph vessels, lines insides of certain organs (called endothelium in this case)

• Lines alveoli of lungs• Easily damaged!

(Mesothelium)

Simple Cuboidal

• Single layer of cube-shaped cells attached to basal membrane

• Covers ovaries, lines tubes and ducts of kidneys, certain glands such as pancreas, salivary glands and liver

• Can be used to secrete glandular products or reabsorb materials such as water (in kidneys)

Simple Columnar

• Single layer of elongated cells, attached to basal membrane

• Cells may or may not be ciliated on their apical surface

• Nonciliated simple columnar epithelia lines the uterus, parts of the GI tract and

• Can secrete digestive juices• Because of thickness, they protect underlying tissues• Ciliated simple columnar epithelia lines the fallopian

tubes, to move eggs• Some line intestines and have villi and microvilli to

increase surface are for absorption

Pseudostratified Ciliated Columnar

•Appears stratified, but is not•Apical surface of cells have cilia•Line respiratory tract•Contain special cells called goblet cells that secrete mucous to trap dust and microorganisms•Mucociliary exhalator

Stratified Squamous Epithelium

• Many layers of squamous cells, so relatively thick• Cells at apical surface are flattened and buildup a

protein called keratin, which protects them from water damage, microorganisms, etc. Cell division occurs in deeper layers where cells are cuboidal or columnar

• Upper layer of skin (keratinized)- tough, dead• Oral cavities, throat, esophagus, vagina, anal

canal – all non-keratinized; upper layer cells are soft, alive.

Stratified Squamous

Stratified Columnar

• Cells at apical end tend to be columnar (elongated) whereas cells at the basal level are cuboidal in shape

• Line the vas deferens, male urethra and areas of the pharynx

Extracellular Matrix (ECM)• The extracellular matrix is basically connective tissue that

– provides structural support and anchorage to the cells in addition to– performs various other important functions.

• Extracellular matrix includes the– interstitial matrix and the – basement membrane. Basement membranes are a sheet-like layer on

which various epithelial cells rest.

• Interstitial matrix is present between various cells (i.e., in the intercellular spaces).

• Fibroblasts are cells found in the ECM. They make, glycosaminoglycans, collagen, reticular and elastic fibers, and glycoproteins found in the extracellular matrix.

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Integrins• Integrins are cell surface receptors that interact

with the extracellular matrix (ECM) and mediate various intracellular signals.

• These are integral membrane proteins – comprised of a single alpha helix.

• Integrin plays a role in the attachment of cells to other cells, and also plays a role in the attachment of a cell to the extracellular matrix.

• Integrin also plays a role in signal transduction, a process by which a cell transforms one kind of signal or stimulus into another.

Fibroblasts – the cells in found in connective tissue

• Fibroblast synthesize several different types of fibers :

1.Collagen - connecting and supporting fibers, which is a major component of skin, tendons, ligaments, and bones

2.elastic fibers, which are found, for example, in the walls of large blood vessels

3.reticular fibers, which form networks inside solid organs, such as the liver.

Interstitial Fluid

• This is a fluid that fills all the spaces between cells of all tissues

• It is needed for the exchange of nutrients and wastes from capillaries and cells (It is a good vehicle for the transport of all these chemicals)

Connective Tissue• Connective tissue binds together, supports, and

protects the other three kinds of tissue.

• Unlike epithelial tissue cells, the cells of connective tissue are widely separated from one another by large amounts of intercellular material, the matrix, which anchors and supports the tissue.

• The matrix comprises a :– ground substance, which is more or less fluid and

amorphous (formless), and– fibers synthesized by the tissue cells.

Connective Tissue

Categories

1. Loose connective tissue2. Dense connective tissue (fibrous connective)3. Adipose tissue4. Cartilage5. Bone6. Blood

Connective Tissue, cont’d.

Loose Connective Tissue

• Forms thin membranes throughout body, • Cells are mainly fibroblasts separated by a a gel-like

substance made up of loosely packed collagen and elastin fibers which the fibroblasts secrete

Found between muscles, under skin,under epithelial tissueCONTAINS MANY BLOOD VESSELS – which supplies blood to epithelial cells

Dense Connective Tissue• Closely packed fibers of elastin and collagen fibers,

arranged in parallel bundles• Only a few cells inside; mainly fibroblasts• Found in tendons (attach muscle to bone), ligaments

(attach bone to bone)

Adipose Tissue

•Two types of adipose cells are found in fat tissues, white and brown adipocytes.  These adipose cell types vary in their ability to mobilize energy from stored fat.  Brown fat cells are smaller and produce heat rather than ATP.  Brown fat is more typical in infants, being replaced gradually by white fat as we age.  In both cell types fat droplets enlarge to push nuclei and cytoplasm to the periphery.

Cartilage• Rigid, structural model for

developing bones – as children mature into adults, more and more cartilage gets replaced by bone

• The matrix is mainly collagen fibers embedded in a gel-like ground substance which is made of protein-carbohydrates like chondroitin sulfate and water

• Chondrocytes (collagen and condroitin secreting cells) lie in the matrix in small cavities called lacunae

Cartilage, cont’d.• Cartilage lacks blood supply• Cartilage heals slowly and chondrocytes do not

often divide (lack of blood supply) • 3 Types:

– Hyaline - Most common• Glass-like• Found on ends of bones

» End of nose

» Rings in respiratory passages (trachea)

» Embryonic skeleton – template for bone development

– Elastic – • Very flexible, found in the epiglottis and “skeleton” of external

ear

– Fibrocartilage – intervertebral discs, pubic symphysis

Bone (Osseous Tissue)

• Most rigid connective tissue

• Rigidity due to mineral salts such as calcium phosphate and calcium carbonate in its matrix

• Bone also contains collagen

• Contains red and yellow marrow which forms blood cells, stores and releases inorganic salts

Bone Tissue – active, living tissue!

• Consists of concentric layers called lamellae, around central canals or Haversian canals

• Each bone unit around a central canal is called an osteon or Haversian system

• Each central canal contains blood vessels

• Chambers called lacunae (lacuna) contain osteocytes which used to be bone-making osteoblasts that have become entrapped in their own secretions.

• Osteocytes extend their cellular extensions into the bone matrix through fine tubes called canaliculi

• The cell extensions form gap junctions with each other - this way nutrients can pass from the blood vessels to all bone cells quickly

Blood• Various cell types found in a liquid matrix called

plasma

– Erythrocytes (RBCs)• Transport O2, CO2• Stay within blood vessels

– Leukocytes (WBCs)• Fight infection (immune system)• Can move from blood vessels to connective tissues

– Platelets (Cell fragments)• Help with clotting

• Most blood cells are produced in hematopoietic tissue like red marrow

Platelets

White Blood Cell

Red Blood Cells

Muscle Tissue

• Skeletal Muscle (voluntary muscles - striated)

• Smooth Muscle (involuntary muscles – non-striated)

• Cardiac Muscle

Skeletal Muscle– Attach bones– Movement can be controlled by us– Long and narrow cells (Muscle fiber) containing

myofibrils made of actin and myosin filaments– The myofibrils have alternating light and dark

striations– Cells are multinucleated and have many

mitochondria– Actin and myosin protein filaments in cells slide past

each other in response to nerve impulses and cause muscle to contract and resume its original shape.

Skeletal Muscle Dissected

(Muscle Cell)

(Cytoplasm of a muscle cell)(Plasma membrane of a muscle cell)

(Group of Filaments)

(Threads of Myosin and actin proteins)(A bundle of muscle cells)

Smooth Muscle

• Called smooth because it lacks striations

• Cells shorter than skeletal muscle cells

• Spindle-shaped

• Single, central nucleus

• Forms muscles of the digestive tract, uterus, urinary bladder, blood vessels, etc.

• Cannot be controlled – involuntary contractions called peristalsis

Smooth Muscle Fibers cells)

Muscle Tissue, cont’d.

• Alternating contractions of circular and longitudinal muscles move food along the digestive tract, a process known as peristalsis.

• Similar arrangements of muscles are involved in many other animal functions, including, for example, the locomotion of the earthworm.

Cardiac MuscleCardiac Muscle

• Found in heart onlyFound in heart only• Cells striated and joined end-to-endCells striated and joined end-to-end• Cells form branchesCells form branches• Single-nucleatedSingle-nucleated• Special intercellular junctions between cells Special intercellular junctions between cells

is called an intercalated disc – found only in is called an intercalated disc – found only in cardiac muscle cellscardiac muscle cells

• Involuntary – can even continue to function Involuntary – can even continue to function without nerve stimuluswithout nerve stimulus

Cardiac Muscle

Branching

Nervous TissueNervous Tissue

• Found in brain, spinal cord (CNS) and peripheral Found in brain, spinal cord (CNS) and peripheral nervous system (PNS)nervous system (PNS)

• Main nerve cells are called neuronsMain nerve cells are called neurons• Highly specializedHighly specialized• Send impulses to each other, muscles and Send impulses to each other, muscles and

glandsglands• Other supporting nervous tissue is made up of Other supporting nervous tissue is made up of

cells called Neuroglial cells, which support cells called Neuroglial cells, which support neurons, provide them with nutrients and help neurons, provide them with nutrients and help with cell-to-cell communicationwith cell-to-cell communication

Membranes and Organs

• Two or more types of tissues working together form an organ or membrane

• Epithelial membranes are composed of epithelial tissue and its underlying connective tissue

• Epithelial membranes are considered organs!

Neurons may reach astonishing lengths. For example, the axon of a single motor neuron may extend from the spinal cord down the whole length of the leg to the toe. Or a sensory neuron may send a dendrite down to the toe and an axon up the entire length of the spinal cord to terminate in the lower part of the brain. In an adult human, such a cell might be close to 2 meters long (5 meters in a giraffe).

Nervous Tissue

1.cell body, which contains the nucleus and much of the metabolic machinery of the cell; the

2.dendrites, usually numerous, short, threadlike cytoplasmic extensions--processes--that receive stimuli from other cells; and the

3.axon, a single long process that carries the nerve impulse away from the cell body to other cells or organs.

– A special junction called a synapse helps transmit a nerve impulse from one neuron to the next.

– Both dendrites and axons are also called nerve fibers.

Metabolic Rate

• The amount of energy an animal uses in a given amount of time is its metabolic rate.

• If one compared animals gram-per-gram, smaller animals require more energy to maintain their body weight.– For example, a gram of mouse requires more energy

than a gram of elephant – even though, overall, the elephant requires more total energy to maintain itself because it is much larger.

What do we all spend our energy on?

Smaller animals use more energy to maintain their body mass

Smaller animals lose heat more easily so:

They use more energy to maintain body temperaturethis in turn requires them to have a higher metabolic rate, which in turn requires more calories, more O2, more eating, faster breathing, faster heart rate and so on.

WHY THIS INVERSE RELATIONSHIP OF BMR PER KG BODY MASS TO BODY SIZE FOR THE SAME ANIMALS?

Heat and Energy are always Lost

• Heat is lost (as mechanical energy) by the body due to all body activities such as digestion, cellular respiration, reproduction, protein synthesis, growth, etc.

• Energy is lost (chemical energy) in chemicals that the body loses in urine, sweat, feces, etc.

Temperature Regulation – Endotherms and Homeotherms

• Mammals and Birds* are endotherms (warm-blooded). This means they generate their own body heat by using the heat produced by their metabolic activities

• In addition to this, most endotherms are homeotherms. This means they maintain a fairly constant body temperature.

• They do this mainly by adjusting the rate of cellular respiration and by using organs such as the skin to warm up and cool down (vasoconstriction, vasodilation and, sweating and shivering)

*some fish, some reptiles and several insect species are “endotherms”, believe it or not, they keep warm by moving.

Thermoregulation – Ectotherms and Poikilotherms

• Most invertebrates are ectotherms – they maintain their body temperature by using the environment – basking in the sun or going into the shade.

• They also tend to be Poikilotherms, which means that their internal temperatures tend to vary widely

Homeotherm, Poikilotherm

Regulators and Conformers • A Regulator is an animal that can maintain

constant internal conditions, even if the external environment fluctuates. – Example – endotherms/homeotherms such as mammals

and birds

• A Conformer is an animal that allows its internal conditions to fluctuate in response to its external environment.– Example – certain fish (large mouth bass) allow their

body temperature to increase or decrease with the outside water temperature. (different from ectotherms/poikilotherms)

– Example – certain marine arthropods are able to change their internal solute (salinity) levels to match that of the ocean around them

Acclimatization (a.ka. Acclimation)Acclimatization (a.ka. Acclimation)

• The process by which an animal adjusts to The process by which an animal adjusts to changes in its environment such as temperature, changes in its environment such as temperature, moisture, food, altitude, daylight changes, etc.moisture, food, altitude, daylight changes, etc.

• Animals do this by growing/shedding fur, Animals do this by growing/shedding fur, increasing or decreasing level of activity, etc.increasing or decreasing level of activity, etc.

• Human examples:Human examples:– Humans need time to adjust to higher elevations by Humans need time to adjust to higher elevations by

producing more RBCs to carry more Oproducing more RBCs to carry more O22

– A move to a different time zone will cause the feeling A move to a different time zone will cause the feeling of “jet lag” or desynchronosis until the body resumes of “jet lag” or desynchronosis until the body resumes its normal 24 hour circadian rhythm.its normal 24 hour circadian rhythm.

BMR and SMR• BMR or Basal Metabolic Rate is the

metabolic rate of a resting, non-growing, non-reproducing, non-stressed endotherm with an empty stomach (fasting) at a particular temperature.

• SMR or Standard Metabolic Rate is the metabolic rate of a resting, non-growing, non-reproducing, non-stressed ectotherm with an empty stomach (fasting) at a particular temperature

Saving Energy• Hibernation allows animals to

conserve energy during the winter when food is short.

• During hibernation, animals drastically lower their metabolism so their stored body fat is used up at a slower rate.

• Torpor – a shorter period of reduced activity and metabolism (temporary hibernation)

Homeostasis –keeping the body’s environment stable(Greek - Unchanging/standing)

Pathway of Homeostatic Regulation

• Receptor – receives environmental stimulus (Thermoreceptors in skin)

• Control center or integration center (Hypothalamus of the Brain)

• Effector – responds to command from control center (Eccrine sweat glands in skin)

Example of Homeostatic Regulation

Positive FeedbackOperates for short periods of time

Example: Blood Clotting

1. Receptors may or may not trigger control center

2. Control center sends message to effectors

3. Effectors create conditions different from the norm

Positive feedback mechanisms produce unstable conditions and therefore are short lived – such as uterine contractions, milk and clot productions

Negative FeedbackMost feedback mechanisms in the body are negative

Example: The Control of Body Temperature (e.g. By perspiration by skin or

shivering by muscles)

1. Receptor senses change or deviation from norm

2. Message sent to Control center which sends message to effectors

3. Effectors return condition back to normal4. As conditions return to normal, effectors are

shut off

I’m so Hot!

Negative feedback mechanisms bring unstable conditions back to normal – they restore stability

Cooling Down• Radiation – heat from body radiates to cooler

surroundings (Passive and active)• Conduction – heat from body transfers

directly to a cooler surface (your rear end warms your seat, so it feels warm to the touch) (Passive)

• Convection – heat from the body escapes to cooler air around the body (Passive and active)

• Evaporation – when sweat evaporates, it takes body heat away with it, cooling the body. (Active effort by body)

Heat Loss, cont’d.In cold weather, blood vessels

constrict, so that heat is retained in the body.

In hot weather, blood vessels dilate, so heat is lost by convection and radiation Evaporative cooling

As water molecules evaporate, they carry some of the heat with them, thus cooling the surface

they leave behind

Warming up

• Increased Cellular Respiration rates – more heat

• Brown Fat – when brown fat is metabolized by the mitochondria, more heat than ATP is generated – babies and many cold-weather mammals store brown fat

• Shivering – produces heat in many mammals and even some insects – prior to flight in the cold, their flight muscles shiver. Some reptiles shiver too.

Insulation• Reduces the flow of heat

between an animal and its environment– Feathers

• In winter, bird feathers are raised - it creates a thicker blanket of trapped air around the bird.

– Hair• Mammals also raise their fur in

response to the cold– Layers of fat (adipose

tissue)• Mammals that lack thick fur

rely on fat insulation When we are cold, the “goose bumps” that form are an evolutionary souvenir of our furry ancestors and their hair-

raising abilities.

THE ENDTHE END