BIO 210 Test 2 Study Guide:
Chapter 4:
1. Define:
Cell – basic unit of life
Tissue – groups of similar cells
Organ – contains 2 or more types of tissues
Organ System – organs that work closely together

2. What are the common functions of:
Epithelial tissue – covers and lines things – protects.
Connective tissue – binds and supports – provides shape and structure.
Muscle Tissue – contraction of muscles and movement.
Nerve Tissue – sends signals and impulses – communication.

3. Be able to compare and contrast examples of each tissue type. Know identifying features of each tissue.
EPITHELIAL TISSUE – 6 KINDS - all have free space at their apical surface.
Simple squamous epithelial tissue – lung and kidney glomerulus – 1 layer of flattened sacs – very thin.
Stratified squamous epithelial tissue – epidermis – multiple layers of flattened sacs.
Simple cuboidal epithelial tissue – kidney tubules – 1 layer – rounded cube shaped cells.
Simple Columnar epithelial tissue – digestive or GI tract – 1 layer – column shaped cells – nuclei at basal membrane.
Pseudostratified columnar epithelial tissue – trachea lining – false multiple layers of column shaped cells – cilia (hair) – goblet cells.
Transitional epithelial tissue – urinary bladder – domed shaped apical cells – looks like forks in the road.

CONNECTIVE TISSUE – 11 KINDS –
Areolar connective tissue – papillary region of the dermis – fibroblasts, collagen and elastic fibers – looks like a spider web.
Adipose connective tissue – hypodermis – adipocyte – looks like bubbles.
Reticular connective tissue – spleen/lymph nodes – looks like a grapevine.
Elastic connective tissue – aorta wall – elastic fibers/dark stain – looks like wavy hair.
Dense regular connective tissue – tendons – fibroblasts/collagen fibers – nuclei between fibers/seems to be going in one direction – often confused with smooth muscle tissue – this is lighter
Dense irregular connective tissue – reticular region of the dermis – fibroblasts/collagen fibers – looks like marbled meat.
Hyaline cartilage connective tissue – trachea – chrondrocyte in lacuna – a lot of empty space in between them.
Elastic cartilage connective tissue – epiglottis/top part of ear – chrondrocyte in lacuna/elastic fibers – dark stain.
Fibrocartilage connective tissue – intervertebral discs – chrondrocyte in lacuna/collagen fibers.

Blood connective tissue – blood – erythrocytes and leukocytes – small bubbles.
Bone connective tissue – bone – osteocytes – looks like a tree trunk.
MUSCLE TISSUE - 3 KINDS –
Skeletal muscle tissue – skeletal muscles (deltoid muscle) – striations/multinucleated/nucleus usually at bottom to make space for contractile tissue – neat, tight pattern.
Cardiac muscle tissue – heart – striations/intercalated disc/branched fibers/rounded nuclei.
Smooth muscle tissue – stomach/reproductive organs – non-striated/a lot of nuclei/darker than dense regular connective tissue/nuclei blend into fibers – are not in between the fibers (looks smeared).

NERVOUS TISSUE – 1 KIND – brain/spinal cord – neurons – look like kites.

4. What tissue types are found in the integument? Where are they found?
- Areolar connective tissue – papillary region of the dermis.
- Adipose connective tissue – hypodermis.
- Dense irregular connective tissue – reticular region of the dermis.
- Stratified squamous epithelial tissue – epidermis.

5. Be able to compare and contrast endocrine and exocrine glands.
Endocrine glands – ductless – secrete hormones – product does not exit the body.
Exocrine glands – ducts – sweat/mucous/oil/salivary glands and digestive enzymes – product exits the body.

6. Cite typical examples of each type of exocrine and endocrine gland.
Endocrine gland – hormones like insulin.
Exocrine gland – Unicellular would be goblet cell.
Multicellular would have a duct and a secretory structure. Can be simple or compound – branched or not - tubular or alveolar or both.

7. Compare and contrast holocrine and mericrine secretion. Be able to recognize examples.
Holocrine – rupture and are replaced by underlying layer – sebaceous glands – lipid soluble products.
Mericrine – exocytosis – saliva, sweat, pancreas - water soluble products.

8. What distinguishes epithelia, mesothelia, and endothelia? Where are each found?
Epithelia – covers and lines – is epithelial tissue.
Mesothelia – is a type of epithelial tissue - in the serous membranes of the ventral cavity – visceral and parietal.
Endothelia – also a type of epithelial tissue – simple squamous cells lining the walls of the heart. Lines cavities.
9. What are microvilli? What are cilli? Where are they found and what purpose do they serve?
Microvilli - increase the surface area of a cell to increase absorption. They are found on the cell membranes of cells in the GI tract/intestines.
Cilli – are hairlike projections on cells that sweep out debris/move along substances – found in trachea.

10. What common cell types are found in each type of connective tissue?
All connective tissues derive from mesenchyme – a type of embryonic connective tissue.

11. What distinguishes mature cells from immature cells in the connective tissue? How does nomenclature (naming) make this distinction?
BLASTS – are immature – they are actively mitotic and secrete ground substances and fibers.
CYTE – are less active and mature – they maintain the health of the matrix.

12. What is the embryonic origin of each general tissue type? How is embryology related to adult structure?
- At first there are 3 primary germ layers of the embryo.
Ectoderm – makes nerve tissue.
Mesoderm - makes muscle and connective tissue and mesenchyme which later makes connective tissues.
Endoderm – is the primary component of epithelial tissue but all 3 layers contribute to it.
-All adult structure arises from the development of the embryo.

13. What distinguishes connective tissue proper, cartilage, bone, and blood?
Function and types of cells.
Connective tissue proper – binds and supports – it has fibroblasts.
Cartilage – protects – it has chondroblasts and cytes.
Bone – protects – it has osteoblasts and cytes.
Blood – is for transportation – it has erythrocytes and leukocytes.

14. What are the steps involved in wound repair?
1) Inflammation – blood vessels dilate - shuts out bacteria – WBC get to site in case they are needed – clotting occurs if necessary.
2) Organization and restored blood supply – blood clot is replaced with granular tissue – fibroblasts make collagen fibers to hold the skin together – organic debris is phagocytized.
3) Regeneration and fibrosis – scab detaches – eventually fully regenerated epithelium will have underlying scar tissue.

Chapter 5:
14. What are the functions of the integument?
Protection – (chemical, physical/mechanical and biological barriers), body temperature regulation, cutaneous sensation, metabolic functions (ex – Vitamin D synthesis), blood reservoir and excretion.

15. What is the function of melanocytes?
They synthesize the pigment melanin in the stratum basale of the epidermis.

16. Compare and contrast eccrine and apocrine sudoriferous glands, mammary and ceruminous glands, and sebaceous glands. Include location, function, initial activation, and method of secretion.
Eccrine and apocrine sudoriferous glands are both sweat glands located in the reticular region of the dermis.
Eccrine glands are smaller than apocrine glands. Merocrine glands with ducts that connect to the outer surface of the skin, they excrete through exocytosis. They are abundant in the palms, soles of the feet and the forehead. Produce sweat which is clear and mostly water.
Apocrine glands are larger than eccrine and produce a yellowish sweat that has a lipid component to it. Also, merocrine glands with ducts that connect to the outer surface of the skin, they excrete through exocytosis. They are activated during puberty and are in the axillary and anogenital regions.
Mammary glands are specialized apocrine glands that secrete breast milk. Also, merocrine glands with ducts that connect to the outer surface of the skin, they excrete through exocytosis.
Ceruminous glands are specialized apocrine glands that secrete cerumin (earwax). Also, merocrine glands with ducts that connect to the outer surface of the skin, they excrete through exocytosis.
Sebaceous glands are oil glands. They are located in the reticular region of the dermis and are associated with a hair follicle. Found all over the body except in thick skin. They secrete sebum, are activated during puberty and secrete by bursting as they are a holocrine gland.

17. Know the function, location, and appearance of the different nerve receptors in the integument.
Meissner’s corpuscle: look like a sperm with a tail on model in the papillary region of the dermis. They are a light touch sensory receptor.
Tactile (Merkel) cell: located at the epidermal-dermal junction these tactile cells look like spiky hemispheres and are associated with disc-like sensory nerve endings that serve as sensory receptors for touch.
Pacinian corpuscle: look like an onion cut in half with concentric rings in the hypodermis. They are a deep touch sensory receptor.
Free nerve endings: sensory receptors located throughout the skin – they let us sense painful stimuli. Look like thin fibers.

18. What are the 5 cell layers of the Epidermis? What are the identifying features of each? What cell types are found in each layer?
From Superficial to Deep:
Stratum Corneum: waterproofed and keratinized, the cells are dead here. The thickest, most outer layer.
Stratum Lucidum: only found in the thick skin of palms and soles of the feet. Clear layer. Flat, dead keratinocytes found here.
Stratum Granulosum: keratinization occurs here. Little black granules on model. Keratohyaline granules are here.
Stratum Spinosum: pre-keratin filaments attached to desmosomes. May find melanin granules, epidermal dendritic cells, and prickle cells (look like they have a spine) here.
Stratum Basale: deepest epidermal layer. Single row of actively mitotic stem cells. Tactile cells may be seen here. Attached to a basement membrane for nutrients and blood supply. Delivers it through to the stratum granulosum – 2 layers above that are cut off from this.

19. What are the major functions of each of the 3 layers of the integument?
Epidermis: made of keratinized stratified squamous epithelial tissue. This is a barrier to the outside world. Waterproof, keratinized, for purposes of protection.
Dermis: made of dense irregular connective tissue. Holds the sensory receptors (like Meissner’s Corpuscles for light touch), a network of blood vessels and nerve fibers, appendages of the skin such as sudoriferous (sweat) glands, sebaceous (oil) glands and hair follicles. Collagen fibers here give skin its strength and resiliency. Elastic fibers give skin its stretch and recoil properties.
Hypodermis: made of adipose connective tissue and Pacinian Corpuscles (deep touch receptors) are here. Mostly a layer of fat for cushioning.

20. Explain why individuals have different skin colors? Factors that affect skin coloration?
Three pigments contribute to skin color. Melanin, carotene, and hemoglobin. Darker skinned people originated at the equator and lighter skin people closer to the poles. Genetics, response to sunlight and disease processes can all affect skin color.

21. What are the functions of hair?
To sense insects on our skin before they bite or sting us. Hair on the scalp protect against physical trauma, heat loss and sunlight. Eyelashes and nose hairs filter particles that could irritate our bodies.

22. What is the function of the arrector pili muscle?
Pulls the hair follicle into an upright position and causes goosebumps. More useful to animals to make themselves look bigger or to trap air to keep warm. Contractions of this muscle also force oil out of the hair follicles from the sebaceous glands.

23. Compare and contrast terminal and vellus hair.
Vellus hair is the pale, fine body hair of females and children.
Terminal hair is the coarser and usually darker hair of the eyebrows and scalp. In puberty terminal hairs appear in the axillary and pubic regions of both sexes and on the chest, face and usually arms and legs of males.

24. Compare and contrast the different forms of skin cancer.
Basal cell carcinoma: least malignant, most common. Stratum basale cells multiply and invade the dermis and hypodermis. Benign – do not metastasize. Cured by surgical excision in 99% of cases.
Squamous cell carcinoma: second most common type. Involves keratinocytes of stratum spinosum. Most common on scalp, ears, lower lip and hands. Good prognosis if treated by radiation or removed surgically. Can metastasize.
Melanoma: most dangerous and rarest. Involves melanocytes. Highly metastatic and resistant to chemotherapy. Treated by wide surgical excision along with immunotherapy.

25. Know the rule of nines. What factors can make a burn critical?
Used to estimate the volume of fluid loss from burns. It divides the body into 11 sections each worth 9%. Anterior and posterior head and neck is 9% (4-1/2% each), anterior and posterior upper limbs is 18% (9% each), anterior and posterior trunk is 36% (18% each), anterior and posterior lower limbs is 36% (18% each) and the remaining 1% is the genital (perineum) region.
Is critical if >25% of the body has 2nd degree burns or >10% of the body has 3rd degree burns or the face, hands or feet bear 3rd degree burns.

26. What are the major risks associated with burns?
The immediate threat to life resulting from severe burns is a catastrophic loss of body fluids containing proteins and electrolytes resulting in dehydration and electrolyte balance. Renal shutdown and circulatory shock can follow.
Severe and widespread infection (sepsis) becomes an issue after the initial crisis passes as the skin is no longer there to be a protective barrier.
Facial burns introduce the possibility of burned respiratory passages, which can swell and cause suffocation.
Burns at joints are also troublesome because scar tissue formation can severely limit joint mobility.
27. Know the different classifications of integumentary glands.
- Sudoriferous (sweat glands) – eccrine and apocrine.
- Sebaceous (oil) glands
- Specialized apocrine – ceruminous and mammary glands.

28. What are the major features of the fingernail?
Free edge (hyponychium), Eponychium – Cuticle, Nail bed, Body of nail, Lunule, Lateral and Proximal nail folds, Root of nail, Nail matrix.

Chapter 6:
29. What are the functions of the skeletal system?
Support, protection, movement, mineral (Ca and P) and growth factor storage, blood cell formation (hematopoiesis), and fat (triglyceride)/energy storage.

30. What are the different cell types found in bone tissues? What distinguishes mature cells from immature cells? Where are each found?
Osteogenic (stem cell), osteoblast, osteocyte, and osteoclast.
Osteogenic cells are mitotically active stem cells found in the membranous periosteum and endosteum. Some of these become osteoblasts and others osteoclasts and some remain stem cells to produce more of the other 2 in the future.
Osteocytes occupy lacunae at the junctions of the lamellae. They are mature and maintain the bone matrix. The 3 other forms are active and therefore immature.
Osteoblasts and osteoclasts do bone remodeling and bone resorbing respectively.

31. Compare and contrast the processes of intramembranous and endochondrial ossification. Which bones form by each process?
Intramembranous ossification forms flat bones (ex) clavicles or cranial bones). Membrane bone develops from fibrous membrane. Grows out from central point – like fontanels (soft spots) on infants fusing together.
Endochondrial ossification forms most of the rest of the skeleton (ex) long bones). Cartilage (endochondral) bone forms by replacing hyaline cartilage. Can’t happen without the framework of hyaline cartilage in place first. (That’s why if the epiphyseal (growth) plate is broken – there is no hyaline cartilage to work from so the bone cannot grow). Bone grows over the hyaline cartilage matrix.

32. What hormones effect bone growth? What cell or process is affected by each?
Growth hormone stimulates epiphyseal plate activity – makes cells at the epiphyseal plate site mitotically active.
Thyroid hormone modulates activity of the growth hormone. Determines your basal metabolic rate.
At puberty, testosterone and estrogens promote adolescent growth spurts and end growth by inducing epiphyseal plate closure at some point. Otherwise bones would just keep growing.

33. How is blood calcium regulated?
When there is not enough blood calcium the parathyroid gland releases parathyroid hormone (PTH. This hormone stimulates the osteoclasts to degrade the bone matrix and release Ca so blood Ca levels go up. It is a negative feedback system.
When there is too much blood calcium the parafollicular cells of the thyroid release the hormone calcitonin. This makes the osteoblasts deposit calcium salts and blood Ca levels drop.

34. What bones are found in the axial skeleton? Appendicular skeleton?
Axial – head, vertebral column and ribs (central column)
Appendicular – arms and legs (appendages)

35. What is the function of the periosteum? Endosteum?
The periosteum is the outer fibrous layer on bone surface. It has an inner osteogenic layer where bone growth occurs. The osteoblasts, osteoclasts and stem cells are in the inner layer. Nerve fibers, nutrient blood vessels and lymphatic vessels enter the bone via the nutrient foramina. Its how blood and nutrients get into the bone.
The endosteum is a kind of periosteum but inside of the bone. They are functionally the same. Delicate membrane on internal surfaces of bone also contain osteoblasts and osteoclasts.
36. Describe the arrangement of the osteon? What features are involved? Where are they found?
The structural unit of compact bone is called an osteon. An osteon is an elongated cylinder oriented parallel to the long axis of the bone. They are like tiny weight bearing pillars. An osteon is a group of hollow tubes of bone matrix, one placed outside the next like the growth rings on a tree. Each matrix tube is a lamella. The lamella has collagen fibers running in one direction on it and the next tube has them running in the opposite direction. This adds to the strength of it to withstand torsion/twisting motions. The bone salts align with the collagen fibers further adding to the strength. Each osteon has a hollow central canal contains blood vessels and nerves.

37. What is hydroxyapatite? Where is it found? How is it formed?
It is inorganic mineral salts. It is 65% of mass in bone tissue. Found embedded with the organic lamella. Mainly Ca Phosphate crystals – give bone their hardness and resistance to compression. They form by aligning with the collagen fibers on the lamella during bone deposit.

38. What is osteoporosis? What factors contribute to this disease?
Osteoporosis refers to loss of bone mass. Bone resorption outpacing bone deposit. The bones become very fragile, porous and susceptible to fracture. Post menopausal women are at particular risk because loss of estrogen causes bone loss. Other factors are a petite body form, diabetes, lack of Ca or Vit. D, immobility or low levels of thyroid stimulating hormone (TSH).

39. What is osteomalacia? Rickets? What factors contribute to these diseases?
Osteomalacia and rickets are when Ca salts are not deposited due to insufficient dietary Ca or Vit. D deficiency. Bones are soft and weak and pain is caused by weight bearing.
Rickets is a childhood disease that causes bowed legs and other bone deformities. It is treatable if caught early enough.

40. What is red marrow? Yellow marrow? Where are each found? Functions?
Red marrow is hematopoietic tissue. It makes red blood cells. It is located in the trabecular cavities of the heads of the femur and humerus and in the DIPLOE (WHAT SPONGY BONE IS CALLED IN FLAT BONES) of flat bones in adults. In infants it is in all spongy bones and medullary cavities.
Yellow marrow is fat. It is stored in the medullary cavities or trabecular cavities that do not have red marrow.

41. What is the function of osteoblasts? Osteoclasts? Osteocytes?
Osteoblasts are bone forming cells. Osteoclasts are bone resorbing cells. Osteocytes maintain the bone matrix.

42. Describe the arrangement of a typical long bone.
The shaft is the disphysis. It is a compact bone collar which surrounds a medullary cavity filled with yellow marrow. On either end are the epiphyses. It has expanded ends, a thin layer of compact bone with spongy bone on the inside. There is hyaline cartilage on each end of the bone. The epiphyseal line (growth plate) is on the epiphyses too on each end.

43. Compare and contrast interstitial and appositional growth.
Two ways that cartilage grows.
Interstitial growth is growth from within – expanding outward from the inside. Chondrocytes divide and secrete new matrix which expands the cartilage from within. Bone growing at both ends – length.
Appositional growth happens when the surface expands outward. Expansion from the surface. Cells secrete matrix against the external face of existing cartilage. Bone thickness.

44. What is hematopoiesis? Where does it occur?
Blood cell formation. Occurs in the marrow cavities of certain bones.

45. What effects does aging have on the skeletal system? How can these effects be minimized?
By age 25 all bones have ossified. Bone mass decreases with age beginning in the 4th decade. In old age, bone resorption predominates. Rate of loss determined by genetics and environmental factors. Nothing you can control about genes but diet and exercise will help the environmental factors.

46. What are the 4 zones found at the epiphyseal plate? What is occurring in each zone?
Proliferation (Growth) – cartilage cells undergo mitosis.
Hypertrophic – older cartilage cells enlarge.
Calcification – matrix becomes calcified, cartilage cells die and matrix begins deteriorating.
Ossification (Osteogenic) – new bone formation is occurring.
(People Have Certain Obligations.)

47. What nutrients are important for healthy bone growth and development?
Protein, Vit. C (helps collagen), Vit.D (helps Ca absorption), Vit. A (cofactor for Vit. C), calcium, phosphorus, magnesium and manganese.

Chapter 7:
48. What are the bones of the axial skeleton? Appendicular?
Axial – skull, vertebral column and thoracic cage
Appendicular – bones of the limbs and their girdles

49. What are the bones of the cranium? Facial bones?
8 Cranial bones: Frontal Bone, 2 Parietal Bones, Occipital Bone, 2 Temporal Bones, Sphenoid Bone and Ethmoid Bone.
14 Facial Bones: Mandible, 2 Maxillary Bones (Maxillae), 2 Zygomatic Bones, 2 Nasal Bones, 2 Lacrimal Bones, 2 Palatine Bones, Vomer and 2 Inferior Nasal Conchae.
(Many Zoo Monkeys Like People In New Vans)

50. What are the 4 sutures of the cranium?
Coronal Suture, Sagittal Suture, Lambdoid Suture and Squamous (Squamosal) Suture.

51. Which bones contribute to the orbit?
Formed by parts of the following 7 bones: Frontal, Sphenoid, Ethmoid, Maxillary, Zygomatic, Lacrimal and Palatine Bones.
(Snakes Like Eating Zoo Monkeys For Pleasure)

52. Which bones have paranasal sinuses?
Found in 4 bones: Frontal, Sphenoid, Ethmoid and Maxillary Bones.
(Snakes Eat More Food)

53. What are the 5 divisions of the vertebral column?
Cervical Vertebrae, Thoracic Vertebrae, Lumbar Vertebrae, Sacrum and Coccyx.
*For the first 3, think of mealtimes 7, 12 and 5. The last two are 5 and 3-5.
54. What are the 4 major curves of the vertebral column? What curves are primary? Secondary?
Two posteriorly convex (Primary) curvatures – Thoracic and Sacral
Two posteriorly concave (Secondary) curvatures – Cervical and Lumbar

55. What are the 3 diseases of vertebral curvature?
Scoliosis – abnormal lateral curve.
Kyphosis – hunchback – exaggerated thoracic curve.
Lordosis – swayback – exaggerated lumbar curve.

56. What are the features of a typical vertebra?
Body or centrum – anterior weight-bearing region
Vertebral Arch – composed of pedicles and laminae that along with the body, enclose the vertebral foramen
Vertebral Foramina – together make up the vertebral canal for the spinal cord
Intervertebral Formina – lateral openings between adjacent vertebrae for spinal nerves
7 Processes per vertebra:
Spinous process – projects posteriorly - nose
Transverse process (2) – project laterally - ears
Superior articular processes (2) – protrude superiorly inferiorly - eyes
Inferior articular processes (2) – protrude inferiorly – double chin
Lamina – cheeks
Pedicle – neck

57. What features are unique to Atlas? Axis?
Atlas is C1. It has no body or spinous process. Consists of anterior and posterior arches and two lateral masses. The superior surfaces of lateral masses articulate with the occipital condyles. It lets you nod your head yes. Up and down.
Axis is C2. The dens projects superiorly into the anterior arch of the atlas. Dens is a pivot for the rotation of atlas. It lets you shake your head no. Back and forth.

58. What are the 3 types of ribs? How many of each type are there? What distinguishes each type?
True Ribs – 7 of them – Pair 1 thru 7 - they are attached directly to the sternum by individual costal cartilages.
False Ribs – 3 of them – Pair 8 thru 10 – attach indirectly to sternum by joining costal cartilage of rib above
Floating False Ribs – 2 of them – Pair 11 thru 12 – have no attachment to the sternum

59. What bones comprise the pectoral girdle? Pelvic girdle?
Pectoral girdle – clavicle and scapula
Pelvic girdle – a pair of hip bones called os coxae or coxal bones – connect to the sacrum posteriorly and to each other anteriorly. Each hip bone consists of 3 fused bones – the ilium, the ischium and the pubis.

60. Compare and contrast the male and female pelvis. *SEE CHART IN POWERPOINTS.
Male pelvis – tilted less forward, adapted for support of male’s heavier build and stronger muscles, cavity of true pelvis is narrow and deep.
Female pelvis – adapted for childbearing, true pelvis (inferior to pelvic brim) defines birth canal; cavity of the true pelvis is broad, shallow and has greater capacity.

61. What features are unique to the hyoid bone?
Not a bone of the skull, does not articulate directly with another bone, site of attachment for muscles of swallowing and speech.

62. What are the 8 carpal bones? Which carpals articulate with the radius in the wrist?
Bottom row proximal to the wrist and thumb first – Scaphoid, Lunate, Triquetrum and Pisiform
Top row distal to the wrist and thumb first – Trapezium, Trapezoid, Capitate and Hamate
(Some Lovers Try Positions That They Can’t Handle)
The scaphoid and the lunate articulate with the radius to form the wrist joint.

63. What are the arches of the foot?
Arches are maintained by interlocking foot bones, ligaments and tendons. There are 3 - Lateral longitudinal arch, medial longitudinal arch, and transverse arch.

64. What are the 4 fontanelles? What function do they serve? Why are they not found in adult skulls?
Anterior, posterior, mastoid (posterolateral), and sphenoid (anterolateral). They are unossified remnants of fibrous membranes between the fetal skull bones. They let the infant’s skull compress somewhat to make passage through the birth canal easier. They are not found in adult skulls because the bones in the infant’s skull fuse together by the time he or she is 2. The sutures seen on the adult skull are where fontanelles used to be.