chapter 12

Question 1

what is connective tissue?

Answer 1

• extremely broad category that corresponds to the four basic types of tissue
  
  • the others being epithelial, nervous, and muscle
• carries out the role of holding the body and its organs together and that it includes bone, blood, and adipose tissue as well as cartilage, ligaments, and tendons

Question 2

what is cartilage?

Answer 2

• a type of connective tissue that does not contain nerves or blood vessels and is primarily made up of cells called chondrocytes which produce collagen, which is a structural protein that is the most common protein by mass in the human body and is found in the extracellular matrix of many types of connective tissue

Question 3

what are ligaments and tendons?

Answer 3

• tough bands of collagenous fibers that connect componenets of the body
  
  • the main difference between ligaments and tendons is simply the kind of connections that they make: ligaments connect bones with other bones, whereas tendons connect muscles with bones

Question 4

what does the skeletal system do?

Answer 4

• provides the body with structural support, and some specific skeletal structures provide important protection for organs

Question 5

how is the skeleton subdivided?

Answer 5

• axial skeleton and the appendicular skeleton
  
  • axial skeleton starts with the skull and runs downward to the bottom of the vertebral column, while the appendicular skeleton accounts for the upper and lower extremities

Question 6

what are the five major types of bones?

Answer 6

• long bones
• flat bones
• short bones
• sesamoid bones
• irregular bones

Question 7

what are joints?

Answer 7

• where bones meet and can be classified in several different ways

Question 8

what are the different types of joints?

Answer 8

• hinge joint
• pivot joint
• saddle joint
• ball-and-socket joint
• plane joint
• condyloid joint
• synovial joints- freely movable joints and have a synovial cavity
• fibrous joints- allows little to no motion (synarthosis)
• ampiarthrosis- in between synovial and fibrous

Question 9

what is the exoskeleton and endoskeleton?

Answer 9

• exoskeleton- a tough “shell” that provides structural support on the outside of the body
• endoskeleton- skeletal system that provides structural support from within the body

Question 10

what are the non-cellular components of the bone?

Answer 10

• the matrix of the bone, which consists of water, collagen fibers, and crystallized minerals, and can be thought of as a storage depot of sorts for calcium and phosphate

Question 11

what are the cellular components of the bone?

Answer 11

• quite diverse and include epithelial, adipose, and nervous tissue as well as cells and structures unique to the bones

Question 12

what are osteoblasts and osteoclasts?

Answer 12

• osteoblasts are cells that produce hydroxyapatite and deposit it into the bone matrix
• osteoclasts break down matrix mobilizing calcium and phosphate if serum levels of those minerals are too low

Question 13

what hormones regulate osteoclast and osteoblast activity?

Answer 13

• parathyroid hormones and calcitrol (a derivative of vitamin D) and they work to increase blood calcium levels through various mechanisms
• calcitonin comes into play when serum levels of calcium are too high (released by the thyroid)

Question 14

what are the different types of bone tissue?

Answer 14

• compact bone/ cortical bone
• cancellous/spongy/trabecular bone

Question 15

where is bone marrow found?

Answer 15

• primarily contained in the flat bones and the heads of the long bones
  
  • it is the location of homatopoiesis (creation of blood) and creates WBC
  • red bone marrow= homatopoiesis
  • yellow bone marrow= adipocytes

Question 16

what are muscles?

Answer 16

• what puts our bodies into motion, including voluntary activities and involuntary but physiologically essential activities

Question 17

what are the three basic types of msucle?

Answer 17

• skeletal
• smooth
• cardiac

Question 18

muscle cells (myocytes) are also known as?

Answer 18

• muscle fibers

Question 19

what are myocytes?

Answer 19

• long tubular cells that primarily contain myofibrils- long, rod-like bundles of actin, myosin and other proteins
  
  • actin and myosin form thin and thick filaments respectively, which are organized into repeating units called sarcomeres (when sarcomeres contract they produce muscle contraction)
• the sarcoplasmic reticulum corressponds to the smooth endoplasmic retiducul, and the sarcoplasm refers to the cytoplasm, and the cell membrane of a myocyte is known as sarcolemma, and mitochondria in myocytes are reffered to as sarcosomes

Question 20

the sarcoplasm of myocytes aslo contain myoglobin and glycogen which do what?

Answer 20

• myoglobin is a red-coloured protein that stores oxygen with a greater affinity than hemoglobin which allows it to “pull” oxygen from the bloodstream
• the glycogen stores in the sarcoplasm allow the quick mobilization of glucose for anaerobic metabolism

Question 21

what is the function of the sarcoplasmic reticulum (endoplasmic reticulum)?

Answer 21

• wraps around the myofibrils, and has the basic function of storing Ca²⁺ ions at a lower concentration than outside the cell, but at a higher concentration than elsewhere in the cell so it plays a role in mediating the transmission of nerve impulses and the resulting contractions
• in non-smooth muscle, the sarcoplasmic reticulum is in contact with structures known as T-tubules which can be thought of as projections of teh sarcolemma (the cell membrane) that reach toward the center of the cell and they contain abundant ion channels that facilitate the rapid transmission of action potentials that initiate muscle contraction

Question 22

skeletal muscles are innervated by?

Answer 22

• the somatic nervous system so it is under conscious control

Question 23

there are 2 different types of fibers within skeletal muscles:

Answer 23

• red fibers (slow-twitch fibers)- obtain their colour from the presence of abundant reserves of myoglobin and are rich in mitochondria
• white fibers (fast-twitch fibers)- lack those elements, and tend to mobilize glycogen for quick bursts of intense action followed by fatigue

Question 24

what is smooth muscle?

Answer 24

• innervated by the autonomic nervous system so it is not under voluntary control
• non-striated
• contain only one nucleus, and is found towards the center of the cell

Question 25

what is cardiac muscle?

Answer 25

* share some features of smooth and skeletal muscle, but has some unique features * not under voluntary control * has one nucleus, but some have two or more * striated * unique feature is it is connected by structures known as intercalated discs, which connect the cytoplasm of adjacent cardiac muscle cells allowing ions to pass from cell to cell (gap junctions whcih allow action potentials to pass rapidly from one cardiac muscle cell to another)

Question 26

what is myogenic activity?

Answer 26

* the ability to contract even without external neural signaling, is an important characeristic of cardiac muscle (also in smooth muscle too) * ex. SA node

Question 27

what are the essential components in the mechanism of muscle contraction?

Answer 27

* the fundamental unit of contraction is the sarcomere which is defined by a band of thick myosin fibers and half of each of the 2 adjacent bands of thin fibers * sarcomeres are divided into the I-band, A-band, H-zone, Z-line, and M-line * the M-line defines the middle of the sarcomere, running through the middle of the thick filaments * the Z-line defines the edges, running through the middle of the thin filaments * the I-band refers to the region where only thin actin filaments are present * the A-band is everything else, that is the entire region where thick filaments are present, including areas of overlap with the thin filaments * H-zone refers to the area where only thick filaments are present

Question 28

what is the sliding filament model?

Answer 28

* the basic mechanism of contraction is for the interwoven myosin and actin fibers to slip past eachother

Question 29

what is the sliding filament mechanism?

Answer 29

* M-line: if we place a single M-line at the center of our sarcomere fragment as a point of reference, it would not change, but since the whole system is being compressed, the distance between M-lines is decreased * Z-line: as the system is compressed, teh Z-lines move closer together by the same reason * A-band: recall that the A-band is defined as the zone where thick filaments are present, regardless of whether they overlap with thin filaments. since the filaments themselves are not compressed during contraction, the A-band stays the same * I-band and H-zone: these 2 areas are defined by the lack of overlap. recall that the I-band is where only thin filaments are present and the H-zone is where only thick filaments are present. since contraction operates by filaments sliding past eachother, the overall effect of contraction is to increase areas of overlap between actin and myosin filaments, thereby shrinking areas defined by overlap

Question 30

the actin and myosin filaments slide past each toher through what is known as the?

Answer 30

* cross-bridge cycle, in which a cross-bridge is formed between myosin and actin, and a power stroke provides the force of contraction

Question 31

Myosin filaments have?

Answer 31

* so called heads that project from the filament. each head has one site that can bind to ATP and another to actin. Actin filaments have a myosin-binding site that is blocked by the regulatory protein tropomyosin in the absence of Ca²⁺

Question 32

as with any cycle, there is no starting point in the absolute sense, but a relatively straightforward place to start is immediately after?

Answer 32

* a power stoke has happened and a cycle of contraction has ended * at this point, myosin and actin are bound together, and the cycle needs to begin again

Question 33

what is the mechanism of muscle contraction?

Answer 33

* ATP to bind to the myosin head, causing a conformational change that releases it from actin * at this point tropomyosin is free to move back into place to block strong interactions between actin and myosin * the atp molecule is then hydrlyzed to form ADP + P_i. this is a stronglynexergonic reaction and is used to move the myosin head into the "cocked position" and in this position it can interact weakly with actin, but tropomyosin prevents stronger interaction * tropomyosin is ultimately removed by Ca²⁺ through a somewhat complex mechanism: Ca²⁺ binds to a protein knwon as troponin that is located on actin, and the complex formed by Ca²⁺ and troponin causes tropomyosin to dissociate from the actin-myosin binding site * at this point the myosin head can bind tightly to actin * the final step is for the power stroke to happen. this occurs via a conformational change that happens when the P_i is released, resulting in a force of about 2pN * after the powerstroke happens, ADP is released and actin and myosin are essentially stuck together until another ATP binds to myosin so the process can begin again

Question 34

How muscles receive the singal to contract?

Answer 34

* an action potential propagates down a motor (efferent) neuron, until it reaches the nerve terminal at the neuromuscular junction * the neurotransmitter acetylcholine is then released into the neuromuscular junction (the muscle cells innervated by a single neuron knwon as a motor nueron) * acetylcholine binds to receptors on the cell membrane, which is known as the sarcolemma in msucle cells, and the sarcolemma then depolarizes in response * this results in an action potential, and when the action potential reaches the sarcoplasmic reticulum, Ca²⁺ is released into the sarcoplas, (the cytoplasm) * once in the sarcoplasm, Ca²⁺ can bind to troponin, which allows contraction to take place

Question 35

an isolated contraction is known as a?

Answer 35

* twitch, and more coordinated contractions occur in a process known as summation

Question 36

what is summation?

Answer 36

* frequent action potentials mean that muscle fibers do not relax completely between stimuli, and the overall contraction becomes stronger

Question 37

what is skin?

Answer 37

* the largest organ of the body by weight, and plays a crucial role in physiology both by serving as a physical barrier dividing the body from the external environment and by making significant contributions to homeostatic regulation

Question 38

the skin is divided into three major layers called?

Answer 38

* the epidermis- the most external layer * the dermis- the basement membrane which lies underneath * below the dermis is the hypodermis

Question 39

what are the layers of the epidermis?

Answer 39

* divided into 5 layers * the stratum corneum (most external) * the stratum lucidum (only present in the skin on the palm and the soles of the feet) * the stratum granulosum * the stratum spinosum * stratum basale (most internal) * can * lily * give * Sam * Beans

Question 40

which layer most directly provides a physical barreir against the outside world?

Answer 40

* stratum corneum and is made up of corneocytes

Question 41

where are keratinocytes produced?

Answer 41

* skin cells that produce keratin * produced from stem cells in teh stratum basale, and then move upwards into the stratum spinosum where they begin to undergo keratinization and form connections to each other * the stratum spinosum also contains Langerhans cells, which are antigen-presenting dendritic cells that help alert the immune system to pathogens invading the body via the skin (or absoprtion)

Question 42

what kind of cells does the stratum basale contain?

Answer 42

* melanocytes whcih produce melainin and is upregualted in responde to UV damage

Question 43

what is the dermis?

Answer 43

* largely composed of dense connective tissue consisting of collagen and elastic gibers but have a diverse range of cell types * vascular tissue * contains hair follicles and sweat glands as a range of broader sensory cells (ruffini endings which sense stretch, Pacinian corpuscles which sense deep vibration and pressure and Meissner corpuscles which sense gentle touch)

Question 44

what is the hypodermis?

Answer 44

* lies beneath the dermis and its main job is to provide structural and immune support * it provides structural support by containing abundant adipocytes that provide padding and insulation * contains macrophages

Question 45

what is the epidermis?

Answer 45

* provides a physical barrier, and this functionality is enhanced in ceratin parts of the body by the presence of fingernails/toenails and hair and calluses * protects against invasive microorganisms by hosting abundant populations of immune cells in the dermis

Question 46

the skin plays a major role in thermoregulation by:

Answer 46

* the fat layer of the hypodermis provides insulation * sweat glands in teh dermis are a major way to avoid overheating (sweat consistis of water and minerals. the evaporation of sweat on the skin absorbs heat energy from the body, thereby cooling the blood close to the skin) * arterioles that supply the skin can also be dilated to deal with excess heat (bringing more blood close to the skin to be cooled) or constricted to deal with excessively cold temperatures (minimizing blood flow to the skin to conserve heat) * body hair also plays a role in conserving heat in cold conditions. (the arrector pili muscles that surround hair follicles contract, causing the body hairs to become vertical, trapping warm air close to the skin)-pilorection * controlled by the hypothalamus in response to various stimuli